This part of the documentation covers all the interfaces of Flask. For parts where Flask depends on external libraries, we document the most important right here and provide links to the canonical documentation.
class flask.Flask(import_name, static_path=None, static_url_path=None, static_folder='static', template_folder='templates', instance_path=None, instance_relative_config=False, root_path=None)
The flask object implements a WSGI application and acts as the central object. It is passed the name of the module or package of the application. Once it is created it will act as a central registry for the view functions, the URL rules, template configuration and much more.
The name of the package is used to resolve resources from inside the package or the folder the module is contained in depending on if the package parameter resolves to an actual python package (a folder with an __init__.py
file inside) or a standard module (just a .py
file).
For more information about resource loading, see open_resource()
.
Usually you create a Flask
instance in your main module or in the __init__.py
file of your package like this:
from flask import Flask app = Flask(__name__)
About the First Parameter
The idea of the first parameter is to give Flask an idea of what belongs to your application. This name is used to find resources on the filesystem, can be used by extensions to improve debugging information and a lot more.
So it’s important what you provide there. If you are using a single module, __name__
is always the correct value. If you however are using a package, it’s usually recommended to hardcode the name of your package there.
For example if your application is defined in yourapplication/app.py
you should create it with one of the two versions below:
app = Flask('yourapplication') app = Flask(__name__.split('.')[0])
Why is that? The application will work even with __name__
, thanks to how resources are looked up. However it will make debugging more painful. Certain extensions can make assumptions based on the import name of your application. For example the Flask-SQLAlchemy extension will look for the code in your application that triggered an SQL query in debug mode. If the import name is not properly set up, that debugging information is lost. (For example it would only pick up SQL queries in yourapplication.app
and not yourapplication.views.frontend
)
New in version 0.11: The root_path
parameter was added.
New in version 0.8: The instance_path
and instance_relative_config
parameters were added.
New in version 0.7: The static_url_path
, static_folder
, and template_folder
parameters were added.
static_folder
folder.static_url_path
. Defaults to the 'static'
folder in the root path of the application.'templates'
folder in the root path of the application.'instance'
next to the package or module is assumed to be the instance path.True
relative filenames for loading the config are assumed to be relative to the instance path instead of the application root.add_template_filter(f, name=None)
Register a custom template filter. Works exactly like the template_filter()
decorator.
name – the optional name of the filter, otherwise the function name will be used.
add_template_global(f, name=None)
Register a custom template global function. Works exactly like the template_global()
decorator.
New in version 0.10.
name – the optional name of the global function, otherwise the function name will be used.
add_template_test(f, name=None)
Register a custom template test. Works exactly like the template_test()
decorator.
New in version 0.10.
name – the optional name of the test, otherwise the function name will be used.
add_url_rule(rule, endpoint=None, view_func=None, **options)
Connects a URL rule. Works exactly like the route()
decorator. If a view_func is provided it will be registered with the endpoint.
Basically this example:
@app.route('/') def index(): pass
Is equivalent to the following:
def index(): pass app.add_url_rule('/', 'index', index)
If the view_func is not provided you will need to connect the endpoint to a view function like so:
app.view_functions['index'] = index
Internally route()
invokes add_url_rule()
so if you want to customize the behavior via subclassing you only need to change this method.
For more information refer to URL Route Registrations.
Changed in version 0.6: OPTIONS
is added automatically as method.
Changed in version 0.2: view_func
parameter added.
Rule
object. A change to Werkzeug is handling of method options. methods is a list of methods this rule should be limited to (GET
, POST
etc.). By default a rule just listens for GET
(and implicitly HEAD
). Starting with Flask 0.6, OPTIONS
is implicitly added and handled by the standard request handling.after_request(f)
Register a function to be run after each request.
Your function must take one parameter, an instance of response_class
and return a new response object or the same (see process_response()
).
As of Flask 0.7 this function might not be executed at the end of the request in case an unhandled exception occurred.
after_request_funcs = None
A dictionary with lists of functions that should be called after each request. The key of the dictionary is the name of the blueprint this function is active for, None
for all requests. This can for example be used to close database connections. To register a function here, use the after_request()
decorator.
app_context()
Binds the application only. For as long as the application is bound to the current context the flask.current_app
points to that application. An application context is automatically created when a request context is pushed if necessary.
Example usage:
with app.app_context(): ...
New in version 0.9.
app_ctx_globals_class
alias of flask.ctx._AppCtxGlobals
auto_find_instance_path()
Tries to locate the instance path if it was not provided to the constructor of the application class. It will basically calculate the path to a folder named instance
next to your main file or the package.
New in version 0.8.
before_first_request(f)
Registers a function to be run before the first request to this instance of the application.
The function will be called without any arguments and its return value is ignored.
New in version 0.8.
before_first_request_funcs = None
A lists of functions that should be called at the beginning of the first request to this instance. To register a function here, use the before_first_request()
decorator.
New in version 0.8.
before_request(f)
Registers a function to run before each request.
The function will be called without any arguments. If the function returns a non-None value, it’s handled as if it was the return value from the view and further request handling is stopped.
before_request_funcs = None
A dictionary with lists of functions that should be called at the beginning of the request. The key of the dictionary is the name of the blueprint this function is active for, None
for all requests. This can for example be used to open database connections or getting hold of the currently logged in user. To register a function here, use the before_request()
decorator.
blueprints = None
all the attached blueprints in a dictionary by name. Blueprints can be attached multiple times so this dictionary does not tell you how often they got attached.
New in version 0.7.
cli = None
The click command line context for this application. Commands registered here show up in the flask command once the application has been discovered. The default commands are provided by Flask itself and can be overridden.
This is an instance of a click.Group
object.
config = None
The configuration dictionary as Config
. This behaves exactly like a regular dictionary but supports additional methods to load a config from files.
config_class
alias of flask.config.Config
context_processor(f)
Registers a template context processor function.
create_global_jinja_loader()
Creates the loader for the Jinja2 environment. Can be used to override just the loader and keeping the rest unchanged. It’s discouraged to override this function. Instead one should override the jinja_loader()
function instead.
The global loader dispatches between the loaders of the application and the individual blueprints.
New in version 0.7.
create_jinja_environment()
Creates the Jinja2 environment based on jinja_options
and select_jinja_autoescape()
. Since 0.7 this also adds the Jinja2 globals and filters after initialization. Override this function to customize the behavior.
Changed in version 0.11: Environment.auto_reload
set in accordance with TEMPLATES_AUTO_RELOAD
configuration option.
New in version 0.5.
create_url_adapter(request)
Creates a URL adapter for the given request. The URL adapter is created at a point where the request context is not yet set up so the request is passed explicitly.
Changed in version 0.9: This can now also be called without a request object when the URL adapter is created for the application context.
New in version 0.6.
debug
The debug flag. Set this to True
to enable debugging of the application. In debug mode the debugger will kick in when an unhandled exception occurs and the integrated server will automatically reload the application if changes in the code are detected.
This attribute can also be configured from the config with the DEBUG
configuration key. Defaults to False
.
default_config = {'APPLICATION_ROOT': None, 'DEBUG': False, 'EXPLAIN_TEMPLATE_LOADING': False, 'JSONIFY_MIMETYPE': 'application/json', 'JSONIFY_PRETTYPRINT_REGULAR': True, 'JSON_AS_ASCII': True, 'JSON_SORT_KEYS': True, 'LOGGER_HANDLER_POLICY': 'always', 'LOGGER_NAME': None, 'MAX_CONTENT_LENGTH': None, 'PERMANENT_SESSION_LIFETIME': datetime.timedelta(days=31), 'PREFERRED_URL_SCHEME': 'http', 'PRESERVE_CONTEXT_ON_EXCEPTION': None, 'PROPAGATE_EXCEPTIONS': None, 'SECRET_KEY': None, 'SEND_FILE_MAX_AGE_DEFAULT': datetime.timedelta(seconds=43200), 'SERVER_NAME': None, 'SESSION_COOKIE_DOMAIN': None, 'SESSION_COOKIE_HTTPONLY': True, 'SESSION_COOKIE_NAME': 'session', 'SESSION_COOKIE_PATH': None, 'SESSION_COOKIE_SECURE': False, 'SESSION_REFRESH_EACH_REQUEST': True, 'TEMPLATES_AUTO_RELOAD': None, 'TESTING': False, 'TRAP_BAD_REQUEST_ERRORS': False, 'TRAP_HTTP_EXCEPTIONS': False, 'USE_X_SENDFILE': False}
Default configuration parameters.
dispatch_request()
Does the request dispatching. Matches the URL and returns the return value of the view or error handler. This does not have to be a response object. In order to convert the return value to a proper response object, call make_response()
.
Changed in version 0.7: This no longer does the exception handling, this code was moved to the new full_dispatch_request()
.
do_teardown_appcontext(exc=<object object>)
Called when an application context is popped. This works pretty much the same as do_teardown_request()
but for the application context.
New in version 0.9.
do_teardown_request(exc=<object object>)
Called after the actual request dispatching and will call every as teardown_request()
decorated function. This is not actually called by the Flask
object itself but is always triggered when the request context is popped. That way we have a tighter control over certain resources under testing environments.
Changed in version 0.9: Added the exc
argument. Previously this was always using the current exception information.
endpoint(endpoint)
A decorator to register a function as an endpoint. Example:
@app.endpoint('example.endpoint') def example(): return "example"
endpoint – the name of the endpoint
error_handler_spec = None
A dictionary of all registered error handlers. The key is None
for error handlers active on the application, otherwise the key is the name of the blueprint. Each key points to another dictionary where the key is the status code of the http exception. The special key None
points to a list of tuples where the first item is the class for the instance check and the second the error handler function.
To register a error handler, use the errorhandler()
decorator.
errorhandler(code_or_exception)
A decorator that is used to register a function given an error code. Example:
@app.errorhandler(404) def page_not_found(error): return 'This page does not exist', 404
You can also register handlers for arbitrary exceptions:
@app.errorhandler(DatabaseError) def special_exception_handler(error): return 'Database connection failed', 500
You can also register a function as error handler without using the errorhandler()
decorator. The following example is equivalent to the one above:
def page_not_found(error): return 'This page does not exist', 404 app.error_handler_spec[None][404] = page_not_found
Setting error handlers via assignments to error_handler_spec
however is discouraged as it requires fiddling with nested dictionaries and the special case for arbitrary exception types.
The first None
refers to the active blueprint. If the error handler should be application wide None
shall be used.
New in version 0.7: Use register_error_handler()
instead of modifying error_handler_spec
directly, for application wide error handlers.
New in version 0.7: One can now additionally also register custom exception types that do not necessarily have to be a subclass of the HTTPException
class.
code_or_exception – the code as integer for the handler, or an arbitrary exception
extensions = None
a place where extensions can store application specific state. For example this is where an extension could store database engines and similar things. For backwards compatibility extensions should register themselves like this:
if not hasattr(app, 'extensions'): app.extensions = {} app.extensions['extensionname'] = SomeObject()
The key must match the name of the extension module. For example in case of a “Flask-Foo” extension in flask_foo
, the key would be 'foo'
.
New in version 0.7.
full_dispatch_request()
Dispatches the request and on top of that performs request pre and postprocessing as well as HTTP exception catching and error handling.
New in version 0.7.
get_send_file_max_age(filename)
Provides default cache_timeout for the send_file()
functions.
By default, this function returns SEND_FILE_MAX_AGE_DEFAULT
from the configuration of current_app
.
Static file functions such as send_from_directory()
use this function, and send_file()
calls this function on current_app
when the given cache_timeout is None
. If a cache_timeout is given in send_file()
, that timeout is used; otherwise, this method is called.
This allows subclasses to change the behavior when sending files based on the filename. For example, to set the cache timeout for .js files to 60 seconds:
class MyFlask(flask.Flask): def get_send_file_max_age(self, name): if name.lower().endswith('.js'): return 60 return flask.Flask.get_send_file_max_age(self, name)
New in version 0.9.
property got_first_request
This attribute is set to True
if the application started handling the first request.
New in version 0.8.
handle_exception(e)
Default exception handling that kicks in when an exception occurs that is not caught. In debug mode the exception will be re-raised immediately, otherwise it is logged and the handler for a 500 internal server error is used. If no such handler exists, a default 500 internal server error message is displayed.
New in version 0.3.
handle_http_exception(e)
Handles an HTTP exception. By default this will invoke the registered error handlers and fall back to returning the exception as response.
New in version 0.3.
handle_url_build_error(error, endpoint, values)
Handle BuildError
on url_for()
.
handle_user_exception(e)
This method is called whenever an exception occurs that should be handled. A special case are HTTPException
s which are forwarded by this function to the handle_http_exception()
method. This function will either return a response value or reraise the exception with the same traceback.
New in version 0.7.
property has_static_folder
This is True
if the package bound object’s container has a folder for static files.
New in version 0.5.
init_jinja_globals()
Deprecated. Used to initialize the Jinja2 globals.
Changed in version 0.7: This method is deprecated with 0.7. Override create_jinja_environment()
instead.
New in version 0.5.
inject_url_defaults(endpoint, values)
Injects the URL defaults for the given endpoint directly into the values dictionary passed. This is used internally and automatically called on URL building.
New in version 0.7.
instance_path = None
Holds the path to the instance folder.
New in version 0.8.
iter_blueprints()
Iterates over all blueprints by the order they were registered.
New in version 0.11.
jinja_env
The Jinja2 environment used to load templates.
jinja_environment
alias of flask.templating.Environment
jinja_loader
The Jinja loader for this package bound object.
New in version 0.5.
jinja_options = {'extensions': ['jinja2.ext.autoescape', 'jinja2.ext.with_']}
Options that are passed directly to the Jinja2 environment.
json_decoder
alias of flask.json.JSONDecoder
json_encoder
alias of flask.json.JSONEncoder
log_exception(exc_info)
Logs an exception. This is called by handle_exception()
if debugging is disabled and right before the handler is called. The default implementation logs the exception as error on the logger
.
New in version 0.8.
property logger
A logging.Logger
object for this application. The default configuration is to log to stderr if the application is in debug mode. This logger can be used to (surprise) log messages. Here some examples:
app.logger.debug('A value for debugging') app.logger.warning('A warning occurred (%d apples)', 42) app.logger.error('An error occurred')
New in version 0.3.
logger_name
The name of the logger to use. By default the logger name is the package name passed to the constructor.
New in version 0.4.
make_config(instance_relative=False)
Used to create the config attribute by the Flask constructor. The instance_relative
parameter is passed in from the constructor of Flask (there named instance_relative_config
) and indicates if the config should be relative to the instance path or the root path of the application.
New in version 0.8.
make_default_options_response()
This method is called to create the default OPTIONS
response. This can be changed through subclassing to change the default behavior of OPTIONS
responses.
New in version 0.7.
make_null_session()
Creates a new instance of a missing session. Instead of overriding this method we recommend replacing the session_interface
.
New in version 0.7.
make_response(rv)
Converts the return value from a view function to a real response object that is an instance of response_class
.
The following types are allowed for rv
:
the object is returned unchanged | |
a response object is created with the string as body | |
| a response object is created with the string encoded to utf-8 as body |
a WSGI function | the function is called as WSGI application and buffered as response object |
A tuple in the form |
rv – the return value from the view function
Changed in version 0.9: Previously a tuple was interpreted as the arguments for the response object.
make_shell_context()
Returns the shell context for an interactive shell for this application. This runs all the registered shell context processors.
New in version 0.11.
name
The name of the application. This is usually the import name with the difference that it’s guessed from the run file if the import name is main. This name is used as a display name when Flask needs the name of the application. It can be set and overridden to change the value.
New in version 0.8.
open_instance_resource(resource, mode='rb')
Opens a resource from the application’s instance folder (instance_path
). Otherwise works like open_resource()
. Instance resources can also be opened for writing.
open_resource(resource, mode='rb')
Opens a resource from the application’s resource folder. To see how this works, consider the following folder structure:
/myapplication.py /schema.sql /static /style.css /templates /layout.html /index.html
If you want to open the schema.sql
file you would do the following:
with app.open_resource('schema.sql') as f: contents = f.read() do_something_with(contents)
open_session(request)
Creates or opens a new session. Default implementation stores all session data in a signed cookie. This requires that the secret_key
is set. Instead of overriding this method we recommend replacing the session_interface
.
request – an instance of request_class
.
permanent_session_lifetime
A timedelta
which is used to set the expiration date of a permanent session. The default is 31 days which makes a permanent session survive for roughly one month.
This attribute can also be configured from the config with the PERMANENT_SESSION_LIFETIME
configuration key. Defaults to timedelta(days=31)
preprocess_request()
Called before the actual request dispatching and will call each before_request()
decorated function, passing no arguments. If any of these functions returns a value, it’s handled as if it was the return value from the view and further request handling is stopped.
This also triggers the url_value_preprocessor()
functions before the actual before_request()
functions are called.
property preserve_context_on_exception
Returns the value of the PRESERVE_CONTEXT_ON_EXCEPTION
configuration value in case it’s set, otherwise a sensible default is returned.
New in version 0.7.
process_response(response)
Can be overridden in order to modify the response object before it’s sent to the WSGI server. By default this will call all the after_request()
decorated functions.
Changed in version 0.5: As of Flask 0.5 the functions registered for after request execution are called in reverse order of registration.
response – a response_class
object.
a new response object or the same, has to be an instance of response_class
.
property propagate_exceptions
Returns the value of the PROPAGATE_EXCEPTIONS
configuration value in case it’s set, otherwise a sensible default is returned.
New in version 0.7.
register_blueprint(blueprint, **options)
Registers a blueprint on the application.
New in version 0.7.
register_error_handler(code_or_exception, f)
Alternative error attach function to the errorhandler()
decorator that is more straightforward to use for non decorator usage.
New in version 0.7.
request_class
alias of flask.wrappers.Request
request_context(environ)
Creates a RequestContext
from the given environment and binds it to the current context. This must be used in combination with the with
statement because the request is only bound to the current context for the duration of the with
block.
Example usage:
with app.request_context(environ): do_something_with(request)
The object returned can also be used without the with
statement which is useful for working in the shell. The example above is doing exactly the same as this code:
ctx = app.request_context(environ) ctx.push() try: do_something_with(request) finally: ctx.pop()
Changed in version 0.3: Added support for non-with statement usage and with
statement is now passed the ctx object.
environ – a WSGI environment
response_class
alias of flask.wrappers.Response
route(rule, **options)
A decorator that is used to register a view function for a given URL rule. This does the same thing as add_url_rule()
but is intended for decorator usage:
@app.route('/') def index(): return 'Hello World'
For more information refer to URL Route Registrations.
Rule
object. A change to Werkzeug is handling of method options. methods is a list of methods this rule should be limited to (GET
, POST
etc.). By default a rule just listens for GET
(and implicitly HEAD
). Starting with Flask 0.6, OPTIONS
is implicitly added and handled by the standard request handling.run(host=None, port=None, debug=None, **options)
Runs the application on a local development server.
Do not use run()
in a production setting. It is not intended to meet security and performance requirements for a production server. Instead, see Deployment Options for WSGI server recommendations.
If the debug
flag is set the server will automatically reload for code changes and show a debugger in case an exception happened.
If you want to run the application in debug mode, but disable the code execution on the interactive debugger, you can pass use_evalex=False
as parameter. This will keep the debugger’s traceback screen active, but disable code execution.
It is not recommended to use this function for development with automatic reloading as this is badly supported. Instead you should be using the flask command line script’s run
support.
Keep in Mind
Flask will suppress any server error with a generic error page unless it is in debug mode. As such to enable just the interactive debugger without the code reloading, you have to invoke run()
with debug=True
and use_reloader=False
. Setting use_debugger
to True
without being in debug mode won’t catch any exceptions because there won’t be any to catch.
Changed in version 0.10: The default port is now picked from the SERVER_NAME
variable.
'0.0.0.0'
to have the server available externally as well. Defaults to '127.0.0.1'
.5000
or the port defined in the SERVER_NAME
config variable if present.debug
.werkzeug.serving.run_simple()
for more information.save_session(session, response)
Saves the session if it needs updates. For the default implementation, check open_session()
. Instead of overriding this method we recommend replacing the session_interface
.
SecureCookie
object)response_class
secret_key
If a secret key is set, cryptographic components can use this to sign cookies and other things. Set this to a complex random value when you want to use the secure cookie for instance.
This attribute can also be configured from the config with the SECRET_KEY
configuration key. Defaults to None
.
select_jinja_autoescape(filename)
Returns True
if autoescaping should be active for the given template name. If no template name is given, returns True
.
New in version 0.5.
send_file_max_age_default
A timedelta
which is used as default cache_timeout for the send_file()
functions. The default is 12 hours.
This attribute can also be configured from the config with the SEND_FILE_MAX_AGE_DEFAULT
configuration key. This configuration variable can also be set with an integer value used as seconds. Defaults to timedelta(hours=12)
send_static_file(filename)
Function used internally to send static files from the static folder to the browser.
New in version 0.5.
The secure cookie uses this for the name of the session cookie.
This attribute can also be configured from the config with the SESSION_COOKIE_NAME
configuration key. Defaults to 'session'
session_interface = <flask.sessions.SecureCookieSessionInterface object>
the session interface to use. By default an instance of SecureCookieSessionInterface
is used here.
New in version 0.8.
shell_context_processor(f)
Registers a shell context processor function.
New in version 0.11.
shell_context_processors = None
A list of shell context processor functions that should be run when a shell context is created.
New in version 0.11.
should_ignore_error(error)
This is called to figure out if an error should be ignored or not as far as the teardown system is concerned. If this function returns True
then the teardown handlers will not be passed the error.
New in version 0.10.
property static_folder
The absolute path to the configured static folder.
teardown_appcontext(f)
Registers a function to be called when the application context ends. These functions are typically also called when the request context is popped.
Example:
ctx = app.app_context() ctx.push() ... ctx.pop()
When ctx.pop()
is executed in the above example, the teardown functions are called just before the app context moves from the stack of active contexts. This becomes relevant if you are using such constructs in tests.
Since a request context typically also manages an application context it would also be called when you pop a request context.
When a teardown function was called because of an exception it will be passed an error object.
The return values of teardown functions are ignored.
New in version 0.9.
teardown_appcontext_funcs = None
A list of functions that are called when the application context is destroyed. Since the application context is also torn down if the request ends this is the place to store code that disconnects from databases.
New in version 0.9.
teardown_request(f)
Register a function to be run at the end of each request, regardless of whether there was an exception or not. These functions are executed when the request context is popped, even if not an actual request was performed.
Example:
ctx = app.test_request_context() ctx.push() ... ctx.pop()
When ctx.pop()
is executed in the above example, the teardown functions are called just before the request context moves from the stack of active contexts. This becomes relevant if you are using such constructs in tests.
Generally teardown functions must take every necessary step to avoid that they will fail. If they do execute code that might fail they will have to surround the execution of these code by try/except statements and log occurring errors.
When a teardown function was called because of a exception it will be passed an error object.
The return values of teardown functions are ignored.
Debug Note
In debug mode Flask will not tear down a request on an exception immediately. Instead it will keep it alive so that the interactive debugger can still access it. This behavior can be controlled by the PRESERVE_CONTEXT_ON_EXCEPTION
configuration variable.
teardown_request_funcs = None
A dictionary with lists of functions that are called after each request, even if an exception has occurred. The key of the dictionary is the name of the blueprint this function is active for, None
for all requests. These functions are not allowed to modify the request, and their return values are ignored. If an exception occurred while processing the request, it gets passed to each teardown_request function. To register a function here, use the teardown_request()
decorator.
New in version 0.7.
template_context_processors = None
A dictionary with list of functions that are called without argument to populate the template context. The key of the dictionary is the name of the blueprint this function is active for, None
for all requests. Each returns a dictionary that the template context is updated with. To register a function here, use the context_processor()
decorator.
template_filter(name=None)
A decorator that is used to register custom template filter. You can specify a name for the filter, otherwise the function name will be used. Example:
@app.template_filter() def reverse(s): return s[::-1]
name – the optional name of the filter, otherwise the function name will be used.
template_global(name=None)
A decorator that is used to register a custom template global function. You can specify a name for the global function, otherwise the function name will be used. Example:
@app.template_global() def double(n): return 2 * n
New in version 0.10.
name – the optional name of the global function, otherwise the function name will be used.
template_test(name=None)
A decorator that is used to register custom template test. You can specify a name for the test, otherwise the function name will be used. Example:
@app.template_test() def is_prime(n): if n == 2: return True for i in range(2, int(math.ceil(math.sqrt(n))) + 1): if n % i == 0: return False return True
New in version 0.10.
name – the optional name of the test, otherwise the function name will be used.
test_client(use_cookies=True, **kwargs)
Creates a test client for this application. For information about unit testing head over to Testing Flask Applications.
Note that if you are testing for assertions or exceptions in your application code, you must set app.testing = True
in order for the exceptions to propagate to the test client. Otherwise, the exception will be handled by the application (not visible to the test client) and the only indication of an AssertionError or other exception will be a 500 status code response to the test client. See the testing
attribute. For example:
app.testing = True client = app.test_client()
The test client can be used in a with
block to defer the closing down of the context until the end of the with
block. This is useful if you want to access the context locals for testing:
with app.test_client() as c: rv = c.get('/?vodka=42') assert request.args['vodka'] == '42'
Additionally, you may pass optional keyword arguments that will then be passed to the application’s test_client_class
constructor. For example:
from flask.testing import FlaskClient class CustomClient(FlaskClient): def __init__(self, *args, **kwargs): self._authentication = kwargs.pop("authentication") super(CustomClient,self).__init__( *args, **kwargs) app.test_client_class = CustomClient client = app.test_client(authentication='Basic ....')
See FlaskClient
for more information.
Changed in version 0.11: Added **kwargs
to support passing additional keyword arguments to the constructor of test_client_class
.
New in version 0.7: The use_cookies
parameter was added as well as the ability to override the client to be used by setting the test_client_class
attribute.
Changed in version 0.4: added support for with
block usage for the client.
test_client_class = None
the test client that is used with when test_client
is used.
New in version 0.7.
test_request_context(*args, **kwargs)
Creates a WSGI environment from the given values (see werkzeug.test.EnvironBuilder
for more information, this function accepts the same arguments).
testing
The testing flag. Set this to True
to enable the test mode of Flask extensions (and in the future probably also Flask itself). For example this might activate unittest helpers that have an additional runtime cost which should not be enabled by default.
If this is enabled and PROPAGATE_EXCEPTIONS is not changed from the default it’s implicitly enabled.
This attribute can also be configured from the config with the TESTING
configuration key. Defaults to False
.
trap_http_exception(e)
Checks if an HTTP exception should be trapped or not. By default this will return False
for all exceptions except for a bad request key error if TRAP_BAD_REQUEST_ERRORS
is set to True
. It also returns True
if TRAP_HTTP_EXCEPTIONS
is set to True
.
This is called for all HTTP exceptions raised by a view function. If it returns True
for any exception the error handler for this exception is not called and it shows up as regular exception in the traceback. This is helpful for debugging implicitly raised HTTP exceptions.
New in version 0.8.
update_template_context(context)
Update the template context with some commonly used variables. This injects request, session, config and g into the template context as well as everything template context processors want to inject. Note that the as of Flask 0.6, the original values in the context will not be overridden if a context processor decides to return a value with the same key.
context – the context as a dictionary that is updated in place to add extra variables.
url_build_error_handlers = None
A list of functions that are called when url_for()
raises a BuildError
. Each function registered here is called with error
, endpoint
and values
. If a function returns None
or raises a BuildError
the next function is tried.
New in version 0.9.
url_default_functions = None
A dictionary with lists of functions that can be used as URL value preprocessors. The key None
here is used for application wide callbacks, otherwise the key is the name of the blueprint. Each of these functions has the chance to modify the dictionary of URL values before they are used as the keyword arguments of the view function. For each function registered this one should also provide a url_defaults()
function that adds the parameters automatically again that were removed that way.
New in version 0.7.
url_defaults(f)
Callback function for URL defaults for all view functions of the application. It’s called with the endpoint and values and should update the values passed in place.
url_map = None
The Map
for this instance. You can use this to change the routing converters after the class was created but before any routes are connected. Example:
from werkzeug.routing import BaseConverter class ListConverter(BaseConverter): def to_python(self, value): return value.split(',') def to_url(self, values): return ','.join(super(ListConverter, self).to_url(value) for value in values) app = Flask(__name__) app.url_map.converters['list'] = ListConverter
url_rule_class
alias of werkzeug.routing.Rule
url_value_preprocessor(f)
Registers a function as URL value preprocessor for all view functions of the application. It’s called before the view functions are called and can modify the url values provided.
url_value_preprocessors = None
A dictionary with lists of functions that can be used as URL value processor functions. Whenever a URL is built these functions are called to modify the dictionary of values in place. The key None
here is used for application wide callbacks, otherwise the key is the name of the blueprint. Each of these functions has the chance to modify the dictionary
New in version 0.7.
use_x_sendfile
Enable this if you want to use the X-Sendfile feature. Keep in mind that the server has to support this. This only affects files sent with the send_file()
method.
New in version 0.2.
This attribute can also be configured from the config with the USE_X_SENDFILE
configuration key. Defaults to False
.
view_functions = None
A dictionary of all view functions registered. The keys will be function names which are also used to generate URLs and the values are the function objects themselves. To register a view function, use the route()
decorator.
wsgi_app(environ, start_response)
The actual WSGI application. This is not implemented in __call__
so that middlewares can be applied without losing a reference to the class. So instead of doing this:
app = MyMiddleware(app)
It’s a better idea to do this instead:
app.wsgi_app = MyMiddleware(app.wsgi_app)
Then you still have the original application object around and can continue to call methods on it.
Changed in version 0.7: The behavior of the before and after request callbacks was changed under error conditions and a new callback was added that will always execute at the end of the request, independent on if an error occurred or not. See Callbacks and Errors.
class flask.Blueprint(name, import_name, static_folder=None, static_url_path=None, template_folder=None, url_prefix=None, subdomain=None, url_defaults=None, root_path=None)
Represents a blueprint. A blueprint is an object that records functions that will be called with the BlueprintSetupState
later to register functions or other things on the main application. See Modular Applications with Blueprints for more information.
New in version 0.7.
add_app_template_filter(f, name=None)
Register a custom template filter, available application wide. Like Flask.add_template_filter()
but for a blueprint. Works exactly like the app_template_filter()
decorator.
name – the optional name of the filter, otherwise the function name will be used.
add_app_template_global(f, name=None)
Register a custom template global, available application wide. Like Flask.add_template_global()
but for a blueprint. Works exactly like the app_template_global()
decorator.
New in version 0.10.
name – the optional name of the global, otherwise the function name will be used.
add_app_template_test(f, name=None)
Register a custom template test, available application wide. Like Flask.add_template_test()
but for a blueprint. Works exactly like the app_template_test()
decorator.
New in version 0.10.
name – the optional name of the test, otherwise the function name will be used.
add_url_rule(rule, endpoint=None, view_func=None, **options)
Like Flask.add_url_rule()
but for a blueprint. The endpoint for the url_for()
function is prefixed with the name of the blueprint.
after_app_request(f)
Like Flask.after_request()
but for a blueprint. Such a function is executed after each request, even if outside of the blueprint.
after_request(f)
Like Flask.after_request()
but for a blueprint. This function is only executed after each request that is handled by a function of that blueprint.
app_context_processor(f)
Like Flask.context_processor()
but for a blueprint. Such a function is executed each request, even if outside of the blueprint.
app_errorhandler(code)
Like Flask.errorhandler()
but for a blueprint. This handler is used for all requests, even if outside of the blueprint.
app_template_filter(name=None)
Register a custom template filter, available application wide. Like Flask.template_filter()
but for a blueprint.
name – the optional name of the filter, otherwise the function name will be used.
app_template_global(name=None)
Register a custom template global, available application wide. Like Flask.template_global()
but for a blueprint.
New in version 0.10.
name – the optional name of the global, otherwise the function name will be used.
app_template_test(name=None)
Register a custom template test, available application wide. Like Flask.template_test()
but for a blueprint.
New in version 0.10.
name – the optional name of the test, otherwise the function name will be used.
app_url_defaults(f)
Same as url_defaults()
but application wide.
app_url_value_preprocessor(f)
Same as url_value_preprocessor()
but application wide.
before_app_first_request(f)
Like Flask.before_first_request()
. Such a function is executed before the first request to the application.
before_app_request(f)
Like Flask.before_request()
. Such a function is executed before each request, even if outside of a blueprint.
before_request(f)
Like Flask.before_request()
but for a blueprint. This function is only executed before each request that is handled by a function of that blueprint.
context_processor(f)
Like Flask.context_processor()
but for a blueprint. This function is only executed for requests handled by a blueprint.
endpoint(endpoint)
Like Flask.endpoint()
but for a blueprint. This does not prefix the endpoint with the blueprint name, this has to be done explicitly by the user of this method. If the endpoint is prefixed with a .
it will be registered to the current blueprint, otherwise it’s an application independent endpoint.
errorhandler(code_or_exception)
Registers an error handler that becomes active for this blueprint only. Please be aware that routing does not happen local to a blueprint so an error handler for 404 usually is not handled by a blueprint unless it is caused inside a view function. Another special case is the 500 internal server error which is always looked up from the application.
Otherwise works as the errorhandler()
decorator of the Flask
object.
get_send_file_max_age(filename)
Provides default cache_timeout for the send_file()
functions.
By default, this function returns SEND_FILE_MAX_AGE_DEFAULT
from the configuration of current_app
.
Static file functions such as send_from_directory()
use this function, and send_file()
calls this function on current_app
when the given cache_timeout is None
. If a cache_timeout is given in send_file()
, that timeout is used; otherwise, this method is called.
This allows subclasses to change the behavior when sending files based on the filename. For example, to set the cache timeout for .js files to 60 seconds:
class MyFlask(flask.Flask): def get_send_file_max_age(self, name): if name.lower().endswith('.js'): return 60 return flask.Flask.get_send_file_max_age(self, name)
New in version 0.9.
property has_static_folder
This is True
if the package bound object’s container has a folder for static files.
New in version 0.5.
jinja_loader
The Jinja loader for this package bound object.
New in version 0.5.
make_setup_state(app, options, first_registration=False)
Creates an instance of BlueprintSetupState()
object that is later passed to the register callback functions. Subclasses can override this to return a subclass of the setup state.
open_resource(resource, mode='rb')
Opens a resource from the application’s resource folder. To see how this works, consider the following folder structure:
/myapplication.py /schema.sql /static /style.css /templates /layout.html /index.html
If you want to open the schema.sql
file you would do the following:
with app.open_resource('schema.sql') as f: contents = f.read() do_something_with(contents)
record(func)
Registers a function that is called when the blueprint is registered on the application. This function is called with the state as argument as returned by the make_setup_state()
method.
record_once(func)
Works like record()
but wraps the function in another function that will ensure the function is only called once. If the blueprint is registered a second time on the application, the function passed is not called.
register(app, options, first_registration=False)
Called by Flask.register_blueprint()
to register a blueprint on the application. This can be overridden to customize the register behavior. Keyword arguments from register_blueprint()
are directly forwarded to this method in the options
dictionary.
register_error_handler(code_or_exception, f)
Non-decorator version of the errorhandler()
error attach function, akin to the register_error_handler()
application-wide function of the Flask
object but for error handlers limited to this blueprint.
New in version 0.11.
route(rule, **options)
Like Flask.route()
but for a blueprint. The endpoint for the url_for()
function is prefixed with the name of the blueprint.
send_static_file(filename)
Function used internally to send static files from the static folder to the browser.
New in version 0.5.
property static_folder
The absolute path to the configured static folder.
teardown_app_request(f)
Like Flask.teardown_request()
but for a blueprint. Such a function is executed when tearing down each request, even if outside of the blueprint.
teardown_request(f)
Like Flask.teardown_request()
but for a blueprint. This function is only executed when tearing down requests handled by a function of that blueprint. Teardown request functions are executed when the request context is popped, even when no actual request was performed.
url_defaults(f)
Callback function for URL defaults for this blueprint. It’s called with the endpoint and values and should update the values passed in place.
url_value_preprocessor(f)
Registers a function as URL value preprocessor for this blueprint. It’s called before the view functions are called and can modify the url values provided.
class flask.Request(environ, populate_request=True, shallow=False)
The request object used by default in Flask. Remembers the matched endpoint and view arguments.
It is what ends up as request
. If you want to replace the request object used you can subclass this and set request_class
to your subclass.
The request object is a Request
subclass and provides all of the attributes Werkzeug defines plus a few Flask specific ones.
form
A MultiDict
with the parsed form data from POST
or PUT
requests. Please keep in mind that file uploads will not end up here, but instead in the files
attribute.
args
A MultiDict
with the parsed contents of the query string. (The part in the URL after the question mark).
values
A CombinedMultiDict
with the contents of both form
and args
.
A dict
with the contents of all cookies transmitted with the request.
stream
If the incoming form data was not encoded with a known mimetype the data is stored unmodified in this stream for consumption. Most of the time it is a better idea to use data
which will give you that data as a string. The stream only returns the data once.
headers
The incoming request headers as a dictionary like object.
data
Contains the incoming request data as string in case it came with a mimetype Flask does not handle.
files
A MultiDict
with files uploaded as part of a POST
or PUT
request. Each file is stored as FileStorage
object. It basically behaves like a standard file object you know from Python, with the difference that it also has a save()
function that can store the file on the filesystem.
environ
The underlying WSGI environment.
method
The current request method (POST
, GET
etc.)
path
full_path
script_root
url
base_url
url_root
Provides different ways to look at the current IRI. Imagine your application is listening on the following application root:
http://www.example.com/myapplication
And a user requests the following URI:
http://www.example.com/myapplication/%CF%80/page.html?x=y
In this case the values of the above mentioned attributes would be the following:
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is_xhr
True
if the request was triggered via a JavaScript XMLHttpRequest
. This only works with libraries that support the X-Requested-With
header and set it to XMLHttpRequest
. Libraries that do that are prototype, jQuery and Mochikit and probably some more.
property blueprint
The name of the current blueprint
property endpoint
The endpoint that matched the request. This in combination with view_args
can be used to reconstruct the same or a modified URL. If an exception happened when matching, this will be None
.
get_json(force=False, silent=False, cache=True)
Parses the incoming JSON request data and returns it. By default this function will return None
if the mimetype is not application/json but this can be overridden by the force
parameter. If parsing fails the on_json_loading_failed()
method on the request object will be invoked.
True
the mimetype is ignored.True
this method will fail silently and return None
.True
the parsed JSON data is remembered on the request.property is_json
Indicates if this request is JSON or not. By default a request is considered to include JSON data if the mimetype is application/json or application/*+json.
New in version 0.11.
property json
If the mimetype is application/json this will contain the parsed JSON data. Otherwise this will be None
.
The get_json()
method should be used instead.
property max_content_length
Read-only view of the MAX_CONTENT_LENGTH
config key.
property module
The name of the current module if the request was dispatched to an actual module. This is deprecated functionality, use blueprints instead.
on_json_loading_failed(e)
Called if decoding of the JSON data failed. The return value of this method is used by get_json()
when an error occurred. The default implementation just raises a BadRequest
exception.
Changed in version 0.10: Removed buggy previous behavior of generating a random JSON response. If you want that behavior back you can trivially add it by subclassing.
New in version 0.8.
routing_exception = None
If matching the URL failed, this is the exception that will be raised / was raised as part of the request handling. This is usually a NotFound
exception or something similar.
url_rule = None
The internal URL rule that matched the request. This can be useful to inspect which methods are allowed for the URL from a before/after handler (request.url_rule.methods
) etc.
New in version 0.6.
view_args = None
A dict of view arguments that matched the request. If an exception happened when matching, this will be None
.
class flask.request
To access incoming request data, you can use the global request
object. Flask parses incoming request data for you and gives you access to it through that global object. Internally Flask makes sure that you always get the correct data for the active thread if you are in a multithreaded environment.
This is a proxy. See Notes On Proxies for more information.
The request object is an instance of a Request
subclass and provides all of the attributes Werkzeug defines. This just shows a quick overview of the most important ones.
class flask.Response(response=None, status=None, headers=None, mimetype=None, content_type=None, direct_passthrough=False)
The response object that is used by default in Flask. Works like the response object from Werkzeug but is set to have an HTML mimetype by default. Quite often you don’t have to create this object yourself because make_response()
will take care of that for you.
If you want to replace the response object used you can subclass this and set response_class
to your subclass.
headers
A Headers
object representing the response headers.
status
A string with a response status.
status_code
The response status as integer.
property data
A descriptor that calls get_data()
and set_data()
.
property mimetype
The mimetype (content type without charset etc.)
Sets a cookie. The parameters are the same as in the cookie Morsel
object in the Python standard library but it accepts unicode data, too.
A warning is raised if the size of the cookie header exceeds max_cookie_size
, but the header will still be set.
None
(default) if the cookie should last only as long as the client’s browser session.datetime
object or UNIX timestamp.domain=".example.com"
will set a cookie that is readable by the domain www.example.com
, foo.example.com
etc. Otherwise, a cookie will only be readable by the domain that set it.True
, the cookie will only be available via HTTPSIf you have the Flask.secret_key
set you can use sessions in Flask applications. A session basically makes it possible to remember information from one request to another. The way Flask does this is by using a signed cookie. So the user can look at the session contents, but not modify it unless they know the secret key, so make sure to set that to something complex and unguessable.
To access the current session you can use the session
object:
class flask.session
The session object works pretty much like an ordinary dict, with the difference that it keeps track on modifications.
This is a proxy. See Notes On Proxies for more information.
The following attributes are interesting:
new
True
if the session is new, False
otherwise.
modified
True
if the session object detected a modification. Be advised that modifications on mutable structures are not picked up automatically, in that situation you have to explicitly set the attribute to True
yourself. Here an example:
# this change is not picked up because a mutable object (here # a list) is changed. session['objects'].append(42) # so mark it as modified yourself session.modified = True
permanent
If set to True
the session lives for permanent_session_lifetime
seconds. The default is 31 days. If set to False
(which is the default) the session will be deleted when the user closes the browser.
New in version 0.8.
The session interface provides a simple way to replace the session implementation that Flask is using.
class flask.sessions.SessionInterface
The basic interface you have to implement in order to replace the default session interface which uses werkzeug’s securecookie implementation. The only methods you have to implement are open_session()
and save_session()
, the others have useful defaults which you don’t need to change.
The session object returned by the open_session()
method has to provide a dictionary like interface plus the properties and methods from the SessionMixin
. We recommend just subclassing a dict and adding that mixin:
class Session(dict, SessionMixin): pass
If open_session()
returns None
Flask will call into make_null_session()
to create a session that acts as replacement if the session support cannot work because some requirement is not fulfilled. The default NullSession
class that is created will complain that the secret key was not set.
To replace the session interface on an application all you have to do is to assign flask.Flask.session_interface
:
app = Flask(__name__) app.session_interface = MySessionInterface()
New in version 0.8.
Helpful helper method that returns the cookie domain that should be used for the session cookie if session cookies are used.
Returns True if the session cookie should be httponly. This currently just returns the value of the SESSION_COOKIE_HTTPONLY
config var.
Returns the path for which the cookie should be valid. The default implementation uses the value from the SESSION_COOKIE_PATH
config var if it’s set, and falls back to APPLICATION_ROOT
or uses /
if it’s None
.
Returns True if the cookie should be secure. This currently just returns the value of the SESSION_COOKIE_SECURE
setting.
get_expiration_time(app, session)
A helper method that returns an expiration date for the session or None
if the session is linked to the browser session. The default implementation returns now + the permanent session lifetime configured on the application.
is_null_session(obj)
Checks if a given object is a null session. Null sessions are not asked to be saved.
This checks if the object is an instance of null_session_class
by default.
make_null_session(app)
Creates a null session which acts as a replacement object if the real session support could not be loaded due to a configuration error. This mainly aids the user experience because the job of the null session is to still support lookup without complaining but modifications are answered with a helpful error message of what failed.
This creates an instance of null_session_class
by default.
null_session_class
make_null_session()
will look here for the class that should be created when a null session is requested. Likewise the is_null_session()
method will perform a typecheck against this type.
alias of NullSession
open_session(app, request)
This method has to be implemented and must either return None
in case the loading failed because of a configuration error or an instance of a session object which implements a dictionary like interface + the methods and attributes on SessionMixin
.
pickle_based = False
A flag that indicates if the session interface is pickle based. This can be used by Flask extensions to make a decision in regards to how to deal with the session object.
New in version 0.10.
save_session(app, session, response)
This is called for actual sessions returned by open_session()
at the end of the request. This is still called during a request context so if you absolutely need access to the request you can do that.
Indicates whether a cookie should be set now or not. This is used by session backends to figure out if they should emit a set-cookie header or not. The default behavior is controlled by the SESSION_REFRESH_EACH_REQUEST
config variable. If it’s set to False
then a cookie is only set if the session is modified, if set to True
it’s always set if the session is permanent.
This check is usually skipped if sessions get deleted.
New in version 0.11.
class flask.sessions.SecureCookieSessionInterface
The default session interface that stores sessions in signed cookies through the itsdangerous
module.
static digest_method()
the hash function to use for the signature. The default is sha1
key_derivation = 'hmac'
the name of the itsdangerous supported key derivation. The default is hmac.
open_session(app, request)
This method has to be implemented and must either return None
in case the loading failed because of a configuration error or an instance of a session object which implements a dictionary like interface + the methods and attributes on SessionMixin
.
salt = 'cookie-session'
the salt that should be applied on top of the secret key for the signing of cookie based sessions.
save_session(app, session, response)
This is called for actual sessions returned by open_session()
at the end of the request. This is still called during a request context so if you absolutely need access to the request you can do that.
serializer = <flask.sessions.TaggedJSONSerializer object>
A python serializer for the payload. The default is a compact JSON derived serializer with support for some extra Python types such as datetime objects or tuples.
session_class
alias of SecureCookieSession
class flask.sessions.SecureCookieSession(initial=None)
Base class for sessions based on signed cookies.
class flask.sessions.NullSession(initial=None)
Class used to generate nicer error messages if sessions are not available. Will still allow read-only access to the empty session but fail on setting.
class flask.sessions.SessionMixin
Expands a basic dictionary with an accessors that are expected by Flask extensions and users for the session.
modified = True
for some backends this will always be True
, but some backends will default this to false and detect changes in the dictionary for as long as changes do not happen on mutable structures in the session. The default mixin implementation just hardcodes True
in.
new = False
some session backends can tell you if a session is new, but that is not necessarily guaranteed. Use with caution. The default mixin implementation just hardcodes False
in.
property permanent
this reflects the '_permanent'
key in the dict.
flask.sessions.session_json_serializer = <flask.sessions.TaggedJSONSerializer object>
A customized JSON serializer that supports a few extra types that we take for granted when serializing (tuples, markup objects, datetime).
This object provides dumping and loading methods similar to simplejson but it also tags certain builtin Python objects that commonly appear in sessions. Currently the following extended values are supported in the JSON it dumps:
Notice
The PERMANENT_SESSION_LIFETIME
config key can also be an integer starting with Flask 0.8. Either catch this down yourself or use the permanent_session_lifetime
attribute on the app which converts the result to an integer automatically.
class flask.testing.FlaskClient(*args, **kwargs)
Works like a regular Werkzeug test client but has some knowledge about how Flask works to defer the cleanup of the request context stack to the end of a with
body when used in a with
statement. For general information about how to use this class refer to werkzeug.test.Client
.
Changed in version 0.12: app.test_client()
includes preset default environment, which can be set after instantiation of the app.test_client()
object in client.environ_base
.
Basic usage is outlined in the Testing Flask Applications chapter.
open(*args, **kwargs)
Takes the same arguments as the EnvironBuilder
class with some additions: You can provide a EnvironBuilder
or a WSGI environment as only argument instead of the EnvironBuilder
arguments and two optional keyword arguments (as_tuple
, buffered
) that change the type of the return value or the way the application is executed.
Changed in version 0.5: If a dict is provided as file in the dict for the data
parameter the content type has to be called content_type
now instead of mimetype
. This change was made for consistency with werkzeug.FileWrapper
.
The follow_redirects
parameter was added to open()
.
Additional parameters:
(environ, result)
Client
should follow HTTP redirects.session_transaction(*args, **kwargs)
When used in combination with a with
statement this opens a session transaction. This can be used to modify the session that the test client uses. Once the with
block is left the session is stored back.
with client.session_transaction() as session: session['value'] = 42
Internally this is implemented by going through a temporary test request context and since session handling could depend on request variables this function accepts the same arguments as test_request_context()
which are directly passed through.
To share data that is valid for one request only from one function to another, a global variable is not good enough because it would break in threaded environments. Flask provides you with a special object that ensures it is only valid for the active request and that will return different values for each request. In a nutshell: it does the right thing, like it does for request
and session
.
flask.g
Just store on this whatever you want. For example a database connection or the user that is currently logged in.
Starting with Flask 0.10 this is stored on the application context and no longer on the request context which means it becomes available if only the application context is bound and not yet a request. This is especially useful when combined with the Faking Resources and Context pattern for testing.
Additionally as of 0.10 you can use the get()
method to get an attribute or None
(or the second argument) if it’s not set. These two usages are now equivalent:
user = getattr(flask.g, 'user', None) user = flask.g.get('user', None)
It’s now also possible to use the in
operator on it to see if an attribute is defined and it yields all keys on iteration.
As of 0.11 you can use pop()
and setdefault()
in the same way you would use them on a dictionary.
This is a proxy. See Notes On Proxies for more information.
flask.current_app
Points to the application handling the request. This is useful for extensions that want to support multiple applications running side by side. This is powered by the application context and not by the request context, so you can change the value of this proxy by using the app_context()
method.
This is a proxy. See Notes On Proxies for more information.
flask.has_request_context()
If you have code that wants to test if a request context is there or not this function can be used. For instance, you may want to take advantage of request information if the request object is available, but fail silently if it is unavailable.
class User(db.Model): def __init__(self, username, remote_addr=None): self.username = username if remote_addr is None and has_request_context(): remote_addr = request.remote_addr self.remote_addr = remote_addr
Alternatively you can also just test any of the context bound objects (such as request
or g
for truthness):
class User(db.Model): def __init__(self, username, remote_addr=None): self.username = username if remote_addr is None and request: remote_addr = request.remote_addr self.remote_addr = remote_addr
New in version 0.7.
flask.copy_current_request_context(f)
A helper function that decorates a function to retain the current request context. This is useful when working with greenlets. The moment the function is decorated a copy of the request context is created and then pushed when the function is called.
Example:
import gevent from flask import copy_current_request_context @app.route('/') def index(): @copy_current_request_context def do_some_work(): # do some work here, it can access flask.request like you # would otherwise in the view function. ... gevent.spawn(do_some_work) return 'Regular response'
New in version 0.10.
flask.has_app_context()
Works like has_request_context()
but for the application context. You can also just do a boolean check on the current_app
object instead.
New in version 0.9.
flask.url_for(endpoint, **values)
Generates a URL to the given endpoint with the method provided.
Variable arguments that are unknown to the target endpoint are appended to the generated URL as query arguments. If the value of a query argument is None
, the whole pair is skipped. In case blueprints are active you can shortcut references to the same blueprint by prefixing the local endpoint with a dot (.
).
This will reference the index function local to the current blueprint:
url_for('.index')
For more information, head over to the Quickstart.
To integrate applications, Flask
has a hook to intercept URL build errors through Flask.url_build_error_handlers
. The url_for
function results in a BuildError
when the current app does not have a URL for the given endpoint and values. When it does, the current_app
calls its url_build_error_handlers
if it is not None
, which can return a string to use as the result of url_for
(instead of url_for
’s default to raise the BuildError
exception) or re-raise the exception. An example:
def external_url_handler(error, endpoint, values): "Looks up an external URL when `url_for` cannot build a URL." # This is an example of hooking the build_error_handler. # Here, lookup_url is some utility function you've built # which looks up the endpoint in some external URL registry. url = lookup_url(endpoint, **values) if url is None: # External lookup did not have a URL. # Re-raise the BuildError, in context of original traceback. exc_type, exc_value, tb = sys.exc_info() if exc_value is error: raise exc_type, exc_value, tb else: raise error # url_for will use this result, instead of raising BuildError. return url app.url_build_error_handlers.append(external_url_handler)
Here, error
is the instance of BuildError
, and endpoint
and values
are the arguments passed into url_for
. Note that this is for building URLs outside the current application, and not for handling 404 NotFound errors.
New in version 0.10: The _scheme
parameter was added.
New in version 0.9: The _anchor
and _method
parameters were added.
New in version 0.9: Calls Flask.handle_build_error()
on BuildError
.
True
, an absolute URL is generated. Server address can be changed via SERVER_NAME
configuration variable which defaults to localhost
._external
parameter must be set to True
or a ValueError
is raised. The default behavior uses the same scheme as the current request, or PREFERRED_URL_SCHEME
from the app configuration if no request context is available. As of Werkzeug 0.10, this also can be set to an empty string to build protocol-relative URLs.flask.abort(status, *args, **kwargs)
Raises an HTTPException
for the given status code or WSGI application:
abort(404) # 404 Not Found abort(Response('Hello World'))
Can be passed a WSGI application or a status code. If a status code is given it’s looked up in the list of exceptions and will raise that exception, if passed a WSGI application it will wrap it in a proxy WSGI exception and raise that:
abort(404) abort(Response('Hello World'))
flask.redirect(location, code=302, Response=None)
Returns a response object (a WSGI application) that, if called, redirects the client to the target location. Supported codes are 301, 302, 303, 305, 307, and 308. 300 is not supported because it’s not a real redirect and 304 because it’s the answer for a request with a request with defined If-Modified-Since headers.
New in version 0.10: The class used for the Response object can now be passed in.
New in version 0.6: The location can now be a unicode string that is encoded using the iri_to_uri()
function.
werkzeug.wrappers.Response
if unspecified.flask.make_response(*args)
Sometimes it is necessary to set additional headers in a view. Because views do not have to return response objects but can return a value that is converted into a response object by Flask itself, it becomes tricky to add headers to it. This function can be called instead of using a return and you will get a response object which you can use to attach headers.
If view looked like this and you want to add a new header:
def index(): return render_template('index.html', foo=42)
You can now do something like this:
def index(): response = make_response(render_template('index.html', foo=42)) response.headers['X-Parachutes'] = 'parachutes are cool' return response
This function accepts the very same arguments you can return from a view function. This for example creates a response with a 404 error code:
response = make_response(render_template('not_found.html'), 404)
The other use case of this function is to force the return value of a view function into a response which is helpful with view decorators:
response = make_response(view_function()) response.headers['X-Parachutes'] = 'parachutes are cool'
Internally this function does the following things:
flask.Flask.make_response()
is invoked with it.flask.Flask.make_response()
function as tuple.New in version 0.6.
flask.after_this_request(f)
Executes a function after this request. This is useful to modify response objects. The function is passed the response object and has to return the same or a new one.
Example:
@app.route('/') def index(): @after_this_request def add_header(response): response.headers['X-Foo'] = 'Parachute' return response return 'Hello World!'
This is more useful if a function other than the view function wants to modify a response. For instance think of a decorator that wants to add some headers without converting the return value into a response object.
New in version 0.9.
flask.send_file(filename_or_fp, mimetype=None, as_attachment=False, attachment_filename=None, add_etags=True, cache_timeout=None, conditional=False, last_modified=None)
Sends the contents of a file to the client. This will use the most efficient method available and configured. By default it will try to use the WSGI server’s file_wrapper support. Alternatively you can set the application’s use_x_sendfile
attribute to True
to directly emit an X-Sendfile
header. This however requires support of the underlying webserver for X-Sendfile
.
By default it will try to guess the mimetype for you, but you can also explicitly provide one. For extra security you probably want to send certain files as attachment (HTML for instance). The mimetype guessing requires a filename
or an attachment_filename
to be provided.
ETags will also be attached automatically if a filename
is provided. You can turn this off by setting add_etags=False
.
If conditional=True
and filename
is provided, this method will try to upgrade the response stream to support range requests. This will allow the request to be answered with partial content response.
Please never pass filenames to this function from user sources; you should use send_from_directory()
instead.
Changed in version 0.12: The filename is no longer automatically inferred from file objects. If you want to use automatic mimetype and etag support, pass a filepath via filename_or_fp
or attachment_filename
.
Changed in version 0.12: The attachment_filename
is preferred over filename
for MIME-type detection.
Changed in version 0.9: cache_timeout pulls its default from application config, when None.
Changed in version 0.7: mimetype guessing and etag support for file objects was deprecated because it was unreliable. Pass a filename if you are able to, otherwise attach an etag yourself. This functionality will be removed in Flask 1.0
New in version 0.5: The add_etags
, cache_timeout
and conditional
parameters were added. The default behavior is now to attach etags.
New in version 0.2.
latin-1
. This is relative to the root_path
if a relative path is specified. Alternatively a file object might be provided in which case X-Sendfile
might not work and fall back to the traditional method. Make sure that the file pointer is positioned at the start of data to send before calling send_file()
.True
if you want to send this file with a Content-Disposition: attachment
header.False
to disable attaching of etags.True
to enable conditional responses.None
(default), this value is set by get_send_file_max_age()
of current_app
.Last-Modified
header to this value, a datetime
or timestamp. If a file was passed, this overrides its mtime.flask.send_from_directory(directory, filename, **options)
Send a file from a given directory with send_file()
. This is a secure way to quickly expose static files from an upload folder or something similar.
Example usage:
@app.route('/uploads/<path:filename>') def download_file(filename): return send_from_directory(app.config['UPLOAD_FOLDER'], filename, as_attachment=True)
Sending files and Performance
It is strongly recommended to activate either X-Sendfile
support in your webserver or (if no authentication happens) to tell the webserver to serve files for the given path on its own without calling into the web application for improved performance.
New in version 0.5.
send_file()
.flask.safe_join(directory, *pathnames)
Safely join directory
and zero or more untrusted pathnames
components.
Example usage:
@app.route('/wiki/<path:filename>') def wiki_page(filename): filename = safe_join(app.config['WIKI_FOLDER'], filename) with open(filename, 'rb') as fd: content = fd.read() # Read and process the file content...
NotFound
if one or more passed paths fall out of its boundaries.
flask.escape(s) → markup
Convert the characters &, <, >, ‘, and ” in string s to HTML-safe sequences. Use this if you need to display text that might contain such characters in HTML. Marks return value as markup string.
class flask.Markup
A string that is ready to be safely inserted into an HTML or XML document, either because it was escaped or because it was marked safe.
Passing an object to the constructor converts it to text and wraps it to mark it safe without escaping. To escape the text, use the escape()
class method instead.
>>> Markup('Hello, <em>World</em>!') Markup('Hello, <em>World</em>!') >>> Markup(42) Markup('42') >>> Markup.escape('Hello, <em>World</em>!') Markup('Hello <em>World</em>!')
This implements the __html__()
interface that some frameworks use. Passing an object that implements __html__()
will wrap the output of that method, marking it safe.
>>> class Foo: ... def __html__(self): ... return '<a href="/foo">foo</a>' ... >>> Markup(Foo()) Markup('<a href="/foo">foo</a>')
This is a subclass of the text type (str
in Python 3, unicode
in Python 2). It has the same methods as that type, but all methods escape their arguments and return a Markup
instance.
>>> Markup('<em>%s</em>') % 'foo & bar' Markup('<em>foo & bar</em>') >>> Markup('<em>Hello</em> ') + '<foo>' Markup('<em>Hello</em> <foo>')
classmethod escape(s)
Escape a string. Calls escape()
and ensures that for subclasses the correct type is returned.
unescape()
the markup, remove tags, and normalize whitespace to single spaces.
>>> Markup('Main » <em>About</em>').striptags() 'Main » About'
unescape()
Convert escaped markup back into a text string. This replaces HTML entities with the characters they represent.
>>> Markup('Main » <em>About</em>').unescape() 'Main » <em>About</em>'
flask.flash(message, category='message')
Flashes a message to the next request. In order to remove the flashed message from the session and to display it to the user, the template has to call get_flashed_messages()
.
Changed in version 0.3: category
parameter added.
'message'
for any kind of message, 'error'
for errors, 'info'
for information messages and 'warning'
for warnings. However any kind of string can be used as category.flask.get_flashed_messages(with_categories=False, category_filter=[])
Pulls all flashed messages from the session and returns them. Further calls in the same request to the function will return the same messages. By default just the messages are returned, but when with_categories
is set to True
, the return value will be a list of tuples in the form (category, message)
instead.
Filter the flashed messages to one or more categories by providing those categories in category_filter
. This allows rendering categories in separate html blocks. The with_categories
and category_filter
arguments are distinct:
with_categories
controls whether categories are returned with message text (True
gives a tuple, where False
gives just the message text).category_filter
filters the messages down to only those matching the provided categories.See Message Flashing for examples.
Changed in version 0.9: category_filter
parameter added.
Changed in version 0.3: with_categories
parameter added.
True
to also receive categories.Flask uses simplejson
for the JSON implementation. Since simplejson is provided by both the standard library as well as extension, Flask will try simplejson first and then fall back to the stdlib json module. On top of that it will delegate access to the current application’s JSON encoders and decoders for easier customization.
So for starters instead of doing:
try: import simplejson as json except ImportError: import json
You can instead just do this:
from flask import json
For usage examples, read the json
documentation in the standard library. The following extensions are by default applied to the stdlib’s JSON module:
datetime
objects are serialized as RFC 822 strings.__html__
method (like Markup
) will have that method called and then the return value is serialized as string.The htmlsafe_dumps()
function of this json module is also available as filter called |tojson
in Jinja2. Note that inside script
tags no escaping must take place, so make sure to disable escaping with |safe
if you intend to use it inside script
tags unless you are using Flask 0.10 which implies that:
<script type=text/javascript> doSomethingWith({{ user.username|tojson|safe }}); </script>
Auto-Sort JSON Keys
The configuration variable JSON_SORT_KEYS
(Configuration Handling) can be set to false to stop Flask from auto-sorting keys. By default sorting is enabled and outside of the app context sorting is turned on.
Notice that disabling key sorting can cause issues when using content based HTTP caches and Python’s hash randomization feature.
flask.json.jsonify(*args, **kwargs)
This function wraps dumps()
to add a few enhancements that make life easier. It turns the JSON output into a Response
object with the application/json mimetype. For convenience, it also converts multiple arguments into an array or multiple keyword arguments into a dict. This means that both jsonify(1,2,3)
and jsonify([1,2,3])
serialize to [1,2,3]
.
For clarity, the JSON serialization behavior has the following differences from dumps()
:
dumps()
.dumps()
.dumps()
.Example usage:
from flask import jsonify @app.route('/_get_current_user') def get_current_user(): return jsonify(username=g.user.username, email=g.user.email, id=g.user.id)
This will send a JSON response like this to the browser:
{ "username": "admin", "email": "admin@localhost", "id": 42 }
Changed in version 0.11: Added support for serializing top-level arrays. This introduces a security risk in ancient browsers. See JSON Security for details.
This function’s response will be pretty printed if it was not requested with X-Requested-With: XMLHttpRequest
to simplify debugging unless the JSONIFY_PRETTYPRINT_REGULAR
config parameter is set to false. Compressed (not pretty) formatting currently means no indents and no spaces after separators.
New in version 0.2.
flask.json.dumps(obj, **kwargs)
Serialize obj
to a JSON formatted str
by using the application’s configured encoder (json_encoder
) if there is an application on the stack.
This function can return unicode
strings or ascii-only bytestrings by default which coerce into unicode strings automatically. That behavior by default is controlled by the JSON_AS_ASCII
configuration variable and can be overridden by the simplejson ensure_ascii
parameter.
flask.json.dump(obj, fp, **kwargs)
Like dumps()
but writes into a file object.
flask.json.loads(s, **kwargs)
Unserialize a JSON object from a string s
by using the application’s configured decoder (json_decoder
) if there is an application on the stack.
flask.json.load(fp, **kwargs)
Like loads()
but reads from a file object.
class flask.json.JSONEncoder(*, skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, default=None)
The default Flask JSON encoder. This one extends the default simplejson encoder by also supporting datetime
objects, UUID
as well as Markup
objects which are serialized as RFC 822 datetime strings (same as the HTTP date format). In order to support more data types override the default()
method.
default(o)
Implement this method in a subclass such that it returns a serializable object for o
, or calls the base implementation (to raise a TypeError
).
For example, to support arbitrary iterators, you could implement default like this:
def default(self, o): try: iterable = iter(o) except TypeError: pass else: return list(iterable) return JSONEncoder.default(self, o)
class flask.json.JSONDecoder(*, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, strict=True, object_pairs_hook=None)
The default JSON decoder. This one does not change the behavior from the default simplejson decoder. Consult the json
documentation for more information. This decoder is not only used for the load functions of this module but also Request
.
flask.render_template(template_name_or_list, **context)
Renders a template from the template folder with the given context.
flask.render_template_string(source, **context)
Renders a template from the given template source string with the given context. Template variables will be autoescaped.
flask.get_template_attribute(template_name, attribute)
Loads a macro (or variable) a template exports. This can be used to invoke a macro from within Python code. If you for example have a template named _cider.html
with the following contents:
{% macro hello(name) %}Hello {{ name }}!{% endmacro %}
You can access this from Python code like this:
hello = get_template_attribute('_cider.html', 'hello') return hello('World')
New in version 0.2.
class flask.Config(root_path, defaults=None)
Works exactly like a dict but provides ways to fill it from files or special dictionaries. There are two common patterns to populate the config.
Either you can fill the config from a config file:
app.config.from_pyfile('yourconfig.cfg')
Or alternatively you can define the configuration options in the module that calls from_object()
or provide an import path to a module that should be loaded. It is also possible to tell it to use the same module and with that provide the configuration values just before the call:
DEBUG = True SECRET_KEY = 'development key' app.config.from_object(__name__)
In both cases (loading from any Python file or loading from modules), only uppercase keys are added to the config. This makes it possible to use lowercase values in the config file for temporary values that are not added to the config or to define the config keys in the same file that implements the application.
Probably the most interesting way to load configurations is from an environment variable pointing to a file:
app.config.from_envvar('YOURAPPLICATION_SETTINGS')
In this case before launching the application you have to set this environment variable to the file you want to use. On Linux and OS X use the export statement:
export YOURAPPLICATION_SETTINGS='/path/to/config/file'
On windows use set
instead.
root_path
.from_envvar(variable_name, silent=False)
Loads a configuration from an environment variable pointing to a configuration file. This is basically just a shortcut with nicer error messages for this line of code:
app.config.from_pyfile(os.environ['YOURAPPLICATION_SETTINGS'])
True
if you want silent failure for missing files.bool. True
if able to load config, False
otherwise.
from_json(filename, silent=False)
Updates the values in the config from a JSON file. This function behaves as if the JSON object was a dictionary and passed to the from_mapping()
function.
True
if you want silent failure for missing files.New in version 0.11.
from_mapping(*mapping, **kwargs)
Updates the config like update()
ignoring items with non-upper keys.
New in version 0.11.
from_object(obj)
Updates the values from the given object. An object can be of one of the following two types:
Objects are usually either modules or classes. from_object()
loads only the uppercase attributes of the module/class. A dict
object will not work with from_object()
because the keys of a dict
are not attributes of the dict
class.
Example of module-based configuration:
app.config.from_object('yourapplication.default_config') from yourapplication import default_config app.config.from_object(default_config)
You should not use this function to load the actual configuration but rather configuration defaults. The actual config should be loaded with from_pyfile()
and ideally from a location not within the package because the package might be installed system wide.
See Development / Production for an example of class-based configuration using from_object()
.
obj – an import name or object
from_pyfile(filename, silent=False)
Updates the values in the config from a Python file. This function behaves as if the file was imported as module with the from_object()
function.
True
if you want silent failure for missing files.New in version 0.7: silent
parameter.
get_namespace(namespace, lowercase=True, trim_namespace=True)
Returns a dictionary containing a subset of configuration options that match the specified namespace/prefix. Example usage:
app.config['IMAGE_STORE_TYPE'] = 'fs' app.config['IMAGE_STORE_PATH'] = '/var/app/images' app.config['IMAGE_STORE_BASE_URL'] = 'http://img.website.com' image_store_config = app.config.get_namespace('IMAGE_STORE_')
The resulting dictionary image_store_config
would look like:
{ 'type': 'fs', 'path': '/var/app/images', 'base_url': 'http://img.website.com' }
This is often useful when configuration options map directly to keyword arguments in functions or class constructors.
New in version 0.11.
flask.ext
This module acts as redirect import module to Flask extensions. It was added in 0.8 as the canonical way to import Flask extensions and makes it possible for us to have more flexibility in how we distribute extensions.
If you want to use an extension named “Flask-Foo” you would import it from ext
as follows:
from flask.ext import foo
New in version 0.8.
flask.stream_with_context(generator_or_function)
Request contexts disappear when the response is started on the server. This is done for efficiency reasons and to make it less likely to encounter memory leaks with badly written WSGI middlewares. The downside is that if you are using streamed responses, the generator cannot access request bound information any more.
This function however can help you keep the context around for longer:
from flask import stream_with_context, request, Response @app.route('/stream') def streamed_response(): @stream_with_context def generate(): yield 'Hello ' yield request.args['name'] yield '!' return Response(generate())
Alternatively it can also be used around a specific generator:
from flask import stream_with_context, request, Response @app.route('/stream') def streamed_response(): def generate(): yield 'Hello ' yield request.args['name'] yield '!' return Response(stream_with_context(generate()))
New in version 0.9.
class flask.ctx.RequestContext(app, environ, request=None)
The request context contains all request relevant information. It is created at the beginning of the request and pushed to the _request_ctx_stack
and removed at the end of it. It will create the URL adapter and request object for the WSGI environment provided.
Do not attempt to use this class directly, instead use test_request_context()
and request_context()
to create this object.
When the request context is popped, it will evaluate all the functions registered on the application for teardown execution (teardown_request()
).
The request context is automatically popped at the end of the request for you. In debug mode the request context is kept around if exceptions happen so that interactive debuggers have a chance to introspect the data. With 0.4 this can also be forced for requests that did not fail and outside of DEBUG
mode. By setting 'flask._preserve_context'
to True
on the WSGI environment the context will not pop itself at the end of the request. This is used by the test_client()
for example to implement the deferred cleanup functionality.
You might find this helpful for unittests where you need the information from the context local around for a little longer. Make sure to properly pop()
the stack yourself in that situation, otherwise your unittests will leak memory.
copy()
Creates a copy of this request context with the same request object. This can be used to move a request context to a different greenlet. Because the actual request object is the same this cannot be used to move a request context to a different thread unless access to the request object is locked.
New in version 0.10.
match_request()
Can be overridden by a subclass to hook into the matching of the request.
pop(exc=<object object>)
Pops the request context and unbinds it by doing that. This will also trigger the execution of functions registered by the teardown_request()
decorator.
Changed in version 0.9: Added the exc
argument.
push()
Binds the request context to the current context.
flask._request_ctx_stack
The internal LocalStack
that is used to implement all the context local objects used in Flask. This is a documented instance and can be used by extensions and application code but the use is discouraged in general.
The following attributes are always present on each layer of the stack:
app
the active Flask application.
url_adapter
the URL adapter that was used to match the request.
request
the current request object.
session
the active session object.
g
an object with all the attributes of the flask.g
object.
flashes
an internal cache for the flashed messages.
Example usage:
from flask import _request_ctx_stack def get_session(): ctx = _request_ctx_stack.top if ctx is not None: return ctx.session
class flask.ctx.AppContext(app)
The application context binds an application object implicitly to the current thread or greenlet, similar to how the RequestContext
binds request information. The application context is also implicitly created if a request context is created but the application is not on top of the individual application context.
pop(exc=<object object>)
Pops the app context.
push()
Binds the app context to the current context.
flask._app_ctx_stack
Works similar to the request context but only binds the application. This is mainly there for extensions to store data.
New in version 0.9.
class flask.blueprints.BlueprintSetupState(blueprint, app, options, first_registration)
Temporary holder object for registering a blueprint with the application. An instance of this class is created by the make_setup_state()
method and later passed to all register callback functions.
add_url_rule(rule, endpoint=None, view_func=None, **options)
A helper method to register a rule (and optionally a view function) to the application. The endpoint is automatically prefixed with the blueprint’s name.
app = None
a reference to the current application
blueprint = None
a reference to the blueprint that created this setup state.
first_registration = None
as blueprints can be registered multiple times with the application and not everything wants to be registered multiple times on it, this attribute can be used to figure out if the blueprint was registered in the past already.
options = None
a dictionary with all options that were passed to the register_blueprint()
method.
subdomain = None
The subdomain that the blueprint should be active for, None
otherwise.
url_defaults = None
A dictionary with URL defaults that is added to each and every URL that was defined with the blueprint.
url_prefix = None
The prefix that should be used for all URLs defined on the blueprint.
New in version 0.6.
signals.signals_available
True
if the signaling system is available. This is the case when blinker is installed.
The following signals exist in Flask:
flask.template_rendered
This signal is sent when a template was successfully rendered. The signal is invoked with the instance of the template as template
and the context as dictionary (named context
).
Example subscriber:
def log_template_renders(sender, template, context, **extra): sender.logger.debug('Rendering template "%s" with context %s', template.name or 'string template', context) from flask import template_rendered template_rendered.connect(log_template_renders, app)
flask.before_render_template
This signal is sent before template rendering process. The signal is invoked with the instance of the template as template
and the context as dictionary (named context
).
Example subscriber:
def log_template_renders(sender, template, context, **extra): sender.logger.debug('Rendering template "%s" with context %s', template.name or 'string template', context) from flask import before_render_template before_render_template.connect(log_template_renders, app)
flask.request_started
This signal is sent when the request context is set up, before any request processing happens. Because the request context is already bound, the subscriber can access the request with the standard global proxies such as request
.
Example subscriber:
def log_request(sender, **extra): sender.logger.debug('Request context is set up') from flask import request_started request_started.connect(log_request, app)
flask.request_finished
This signal is sent right before the response is sent to the client. It is passed the response to be sent named response
.
Example subscriber:
def log_response(sender, response, **extra): sender.logger.debug('Request context is about to close down. ' 'Response: %s', response) from flask import request_finished request_finished.connect(log_response, app)
flask.got_request_exception
This signal is sent when an exception happens during request processing. It is sent before the standard exception handling kicks in and even in debug mode, where no exception handling happens. The exception itself is passed to the subscriber as exception
.
Example subscriber:
def log_exception(sender, exception, **extra): sender.logger.debug('Got exception during processing: %s', exception) from flask import got_request_exception got_request_exception.connect(log_exception, app)
flask.request_tearing_down
This signal is sent when the request is tearing down. This is always called, even if an exception is caused. Currently functions listening to this signal are called after the regular teardown handlers, but this is not something you can rely on.
Example subscriber:
def close_db_connection(sender, **extra): session.close() from flask import request_tearing_down request_tearing_down.connect(close_db_connection, app)
As of Flask 0.9, this will also be passed an exc
keyword argument that has a reference to the exception that caused the teardown if there was one.
flask.appcontext_tearing_down
This signal is sent when the app context is tearing down. This is always called, even if an exception is caused. Currently functions listening to this signal are called after the regular teardown handlers, but this is not something you can rely on.
Example subscriber:
def close_db_connection(sender, **extra): session.close() from flask import appcontext_tearing_down appcontext_tearing_down.connect(close_db_connection, app)
This will also be passed an exc
keyword argument that has a reference to the exception that caused the teardown if there was one.
flask.appcontext_pushed
This signal is sent when an application context is pushed. The sender is the application. This is usually useful for unittests in order to temporarily hook in information. For instance it can be used to set a resource early onto the g
object.
Example usage:
from contextlib import contextmanager from flask import appcontext_pushed @contextmanager def user_set(app, user): def handler(sender, **kwargs): g.user = user with appcontext_pushed.connected_to(handler, app): yield
And in the testcode:
def test_user_me(self): with user_set(app, 'john'): c = app.test_client() resp = c.get('/users/me') assert resp.data == 'username=john'
New in version 0.10.
flask.appcontext_popped
This signal is sent when an application context is popped. The sender is the application. This usually falls in line with the appcontext_tearing_down
signal.
New in version 0.10.
flask.message_flashed
This signal is sent when the application is flashing a message. The messages is sent as message
keyword argument and the category as category
.
Example subscriber:
recorded = [] def record(sender, message, category, **extra): recorded.append((message, category)) from flask import message_flashed message_flashed.connect(record, app)
New in version 0.10.
class signals.Namespace
An alias for blinker.base.Namespace
if blinker is available, otherwise a dummy class that creates fake signals. This class is available for Flask extensions that want to provide the same fallback system as Flask itself.
signal(name, doc=None)
Creates a new signal for this namespace if blinker is available, otherwise returns a fake signal that has a send method that will do nothing but will fail with a RuntimeError
for all other operations, including connecting.
New in version 0.7.
class flask.views.View
Alternative way to use view functions. A subclass has to implement dispatch_request()
which is called with the view arguments from the URL routing system. If methods
is provided the methods do not have to be passed to the add_url_rule()
method explicitly:
class MyView(View): methods = ['GET'] def dispatch_request(self, name): return 'Hello %s!' % name app.add_url_rule('/hello/<name>', view_func=MyView.as_view('myview'))
When you want to decorate a pluggable view you will have to either do that when the view function is created (by wrapping the return value of as_view()
) or you can use the decorators
attribute:
class SecretView(View): methods = ['GET'] decorators = [superuser_required] def dispatch_request(self): ...
The decorators stored in the decorators list are applied one after another when the view function is created. Note that you can not use the class based decorators since those would decorate the view class and not the generated view function!
classmethod as_view(name, *class_args, **class_kwargs)
Converts the class into an actual view function that can be used with the routing system. Internally this generates a function on the fly which will instantiate the View
on each request and call the dispatch_request()
method on it.
The arguments passed to as_view()
are forwarded to the constructor of the class.
decorators = ()
The canonical way to decorate class-based views is to decorate the return value of as_view(). However since this moves parts of the logic from the class declaration to the place where it’s hooked into the routing system.
You can place one or more decorators in this list and whenever the view function is created the result is automatically decorated.
New in version 0.8.
dispatch_request()
Subclasses have to override this method to implement the actual view function code. This method is called with all the arguments from the URL rule.
methods = None
A list of methods this view can handle.
class flask.views.MethodView
Like a regular class-based view but that dispatches requests to particular methods. For instance if you implement a method called get()
it means it will respond to 'GET'
requests and the dispatch_request()
implementation will automatically forward your request to that. Also options
is set for you automatically:
class CounterAPI(MethodView): def get(self): return session.get('counter', 0) def post(self): session['counter'] = session.get('counter', 0) + 1 return 'OK' app.add_url_rule('/counter', view_func=CounterAPI.as_view('counter'))
dispatch_request(*args, **kwargs)
Subclasses have to override this method to implement the actual view function code. This method is called with all the arguments from the URL rule.
Generally there are three ways to define rules for the routing system:
flask.Flask.route()
decorator.flask.Flask.add_url_rule()
function.flask.Flask.url_map
.Variable parts in the route can be specified with angular brackets (/user/<username>
). By default a variable part in the URL accepts any string without a slash however a different converter can be specified as well by using <converter:name>
.
Variable parts are passed to the view function as keyword arguments.
The following converters are available:
| accepts any text without a slash (the default) |
| accepts integers |
| like |
| like the default but also accepts slashes |
| matches one of the items provided |
| accepts UUID strings |
Custom converters can be defined using flask.Flask.url_map
.
Here are some examples:
@app.route('/') def index(): pass @app.route('/<username>') def show_user(username): pass @app.route('/post/<int:post_id>') def show_post(post_id): pass
An important detail to keep in mind is how Flask deals with trailing slashes. The idea is to keep each URL unique so the following rules apply:
This is consistent with how web servers deal with static files. This also makes it possible to use relative link targets safely.
You can also define multiple rules for the same function. They have to be unique however. Defaults can also be specified. Here for example is a definition for a URL that accepts an optional page:
@app.route('/users/', defaults={'page': 1}) @app.route('/users/page/<int:page>') def show_users(page): pass
This specifies that /users/
will be the URL for page one and /users/page/N
will be the URL for page N
.
Here are the parameters that route()
and add_url_rule()
accept. The only difference is that with the route parameter the view function is defined with the decorator instead of the view_func
parameter.
| the URL rule as string |
| the endpoint for the registered URL rule. Flask itself assumes that the name of the view function is the name of the endpoint if not explicitly stated. |
| the function to call when serving a request to the provided endpoint. If this is not provided one can specify the function later by storing it in the |
| A dictionary with defaults for this rule. See the example above for how defaults work. |
| specifies the rule for the subdomain in case subdomain matching is in use. If not specified the default subdomain is assumed. |
| the options to be forwarded to the underlying |
For internal usage the view functions can have some attributes attached to customize behavior the view function would normally not have control over. The following attributes can be provided optionally to either override some defaults to add_url_rule()
or general behavior:
__name__
: The name of a function is by default used as endpoint. If endpoint is provided explicitly this value is used. Additionally this will be prefixed with the name of the blueprint by default which cannot be customized from the function itself.methods
: If methods are not provided when the URL rule is added, Flask will look on the view function object itself if a methods
attribute exists. If it does, it will pull the information for the methods from there.provide_automatic_options
: if this attribute is set Flask will either force enable or disable the automatic implementation of the HTTP OPTIONS
response. This can be useful when working with decorators that want to customize the OPTIONS
response on a per-view basis.required_methods
: if this attribute is set, Flask will always add these methods when registering a URL rule even if the methods were explicitly overridden in the route()
call.Full example:
def index(): if request.method == 'OPTIONS': # custom options handling here ... return 'Hello World!' index.provide_automatic_options = False index.methods = ['GET', 'OPTIONS'] app.add_url_rule('/', index)
New in version 0.8: The provide_automatic_options
functionality was added.
class flask.cli.FlaskGroup(add_default_commands=True, create_app=None, add_version_option=True, **extra)
Special subclass of the AppGroup
group that supports loading more commands from the configured Flask app. Normally a developer does not have to interface with this class but there are some very advanced use cases for which it makes sense to create an instance of this.
For information as of why this is useful see Custom Scripts.
--version
option.get_command(ctx, name)
Given a context and a command name, this returns a Command
object if it exists or returns None
.
list_commands(ctx)
Returns a list of subcommand names in the order they should appear.
main(*args, **kwargs)
This is the way to invoke a script with all the bells and whistles as a command line application. This will always terminate the application after a call. If this is not wanted, SystemExit
needs to be caught.
This method is also available by directly calling the instance of a Command
.
New in version 3.0: Added the standalone_mode
flag to control the standalone mode.
sys.argv[1:]
is used.sys.argv[0]
."_<prog_name>_COMPLETE"
with prog_name in uppercase.False
they will be propagated to the caller and the return value of this function is the return value of invoke()
.Context
for more information.class flask.cli.AppGroup(name=None, commands=None, **attrs)
This works similar to a regular click Group
but it changes the behavior of the command()
decorator so that it automatically wraps the functions in with_appcontext()
.
Not to be confused with FlaskGroup
.
command(*args, **kwargs)
This works exactly like the method of the same name on a regular click.Group
but it wraps callbacks in with_appcontext()
unless it’s disabled by passing with_appcontext=False
.
group(*args, **kwargs)
This works exactly like the method of the same name on a regular click.Group
but it defaults the group class to AppGroup
.
class flask.cli.ScriptInfo(app_import_path=None, create_app=None)
Help object to deal with Flask applications. This is usually not necessary to interface with as it’s used internally in the dispatching to click. In future versions of Flask this object will most likely play a bigger role. Typically it’s created automatically by the FlaskGroup
but you can also manually create it and pass it onwards as click object.
app_import_path = None
Optionally the import path for the Flask application.
create_app = None
Optionally a function that is passed the script info to create the instance of the application.
data = None
A dictionary with arbitrary data that can be associated with this script info.
load_app()
Loads the Flask app (if not yet loaded) and returns it. Calling this multiple times will just result in the already loaded app to be returned.
flask.cli.with_appcontext(f)
Wraps a callback so that it’s guaranteed to be executed with the script’s application context. If callbacks are registered directly to the app.cli
object then they are wrapped with this function by default unless it’s disabled.
flask.cli.pass_script_info(f)
Marks a function so that an instance of ScriptInfo
is passed as first argument to the click callback.
flask.cli.run_command = <Command run>
Runs a local development server for the Flask application.
This local server is recommended for development purposes only but it can also be used for simple intranet deployments. By default it will not support any sort of concurrency at all to simplify debugging. This can be changed with the –with-threads option which will enable basic multithreading.
The reloader and debugger are by default enabled if the debug flag of Flask is enabled and disabled otherwise.
flask.cli.shell_command = <Command shell>
Runs an interactive Python shell in the context of a given Flask application. The application will populate the default namespace of this shell according to it’s configuration.
This is useful for executing small snippets of management code without having to manually configuring the application.
© 2007–2020 Pallets
Licensed under the BSD 3-clause License.
https://flask.palletsprojects.com/en/0.12.x/api/