tf.Session

A class for running TensorFlow operations.

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Compat aliases for migration

See Migration guide for more details.

tf.compat.v1.Session

tf.Session(
    target='', graph=None, config=None
)

A Session object encapsulates the environment in which Operation objects are executed, and Tensor objects are evaluated. For example:

# Build a graph.
a = tf.constant(5.0)
b = tf.constant(6.0)
c = a * b

# Launch the graph in a session.
sess = tf.compat.v1.Session()

# Evaluate the tensor `c`.
print(sess.run(c))

A session may own resources, such as tf.Variable, tf.queue.QueueBase, and tf.compat.v1.ReaderBase. It is important to release these resources when they are no longer required. To do this, either invoke the tf.Session.close method on the session, or use the session as a context manager. The following two examples are equivalent:

# Using the `close()` method.
sess = tf.compat.v1.Session()
sess.run(...)
sess.close()

# Using the context manager.
with tf.compat.v1.Session() as sess:
  sess.run(...)

The ConfigProto protocol buffer exposes various configuration options for a session. For example, to create a session that uses soft constraints for device placement, and log the resulting placement decisions, create a session as follows:

# Launch the graph in a session that allows soft device placement and
# logs the placement decisions.
sess = tf.compat.v1.Session(config=tf.compat.v1.ConfigProto(
    allow_soft_placement=True,
    log_device_placement=True))

Args
target	(Optional.) The execution engine to connect to. Defaults to using an in-process engine. See Distributed TensorFlow for more examples.
graph	(Optional.) The Graph to be launched (described above).
config	(Optional.) A ConfigProto protocol buffer with configuration options for the session.

Attributes
graph	The graph that was launched in this session.
graph_def	A serializable version of the underlying TensorFlow graph.
sess_str	The TensorFlow process to which this session will connect.

Methods

as_default

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as_default()

Returns a context manager that makes this object the default session.

Use with the with keyword to specify that calls to tf.Operation.run or tf.Tensor.eval should be executed in this session.

c = tf.constant(..)
sess = tf.compat.v1.Session()

with sess.as_default():
  assert tf.compat.v1.get_default_session() is sess
  print(c.eval())

To get the current default session, use tf.compat.v1.get_default_session.

Note: The as_default context manager does not close the session when you exit the context, and you must close the session explicitly.

c = tf.constant(...)
sess = tf.compat.v1.Session()
with sess.as_default():
  print(c.eval())
# ...
with sess.as_default():
  print(c.eval())

sess.close()

Alternatively, you can use with tf.compat.v1.Session(): to create a session that is automatically closed on exiting the context, including when an uncaught exception is raised.

Note: The default session is a property of the current thread. If you create a new thread, and wish to use the default session in that thread, you must explicitly add a with sess.as_default(): in that thread's function.

Note: Entering a with sess.as_default(): block does not affect the current default graph. If you are using multiple graphs, and sess.graph is different from the value of tf.compat.v1.get_default_graph, you must explicitly enter a with sess.graph.as_default(): block to make sess.graph the default graph.

Returns
A context manager using this session as the default session.

close

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close()

Closes this session.

Calling this method frees all resources associated with the session.

Raises
tf.errors.OpError	Or one of its subclasses if an error occurs while closing the TensorFlow session.

list_devices

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list_devices()

Lists available devices in this session.

devices = sess.list_devices()
for d in devices:
  print(d.name)

Where:

Each element in the list has the following properties

• name: A string with the full name of the device. ex: /job:worker/replica:0/task:3/device:CPU:0
• device_type: The type of the device (e.g. CPU, GPU, TPU.)
• memory_limit: The maximum amount of memory available on the device. Note: depending on the device, it is possible the usable memory could be substantially less.

Raises
tf.errors.OpError	If it encounters an error (e.g. session is in an invalid state, or network errors occur).

Returns
A list of devices in the session.

make_callable

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make_callable(
    fetches, feed_list=None, accept_options=False
)

Returns a Python callable that runs a particular step.

The returned callable will take len(feed_list) arguments whose types must be compatible feed values for the respective elements of feed_list. For example, if element i of feed_list is a tf.Tensor, the ith argument to the returned callable must be a numpy ndarray (or something convertible to an ndarray) with matching element type and shape. See tf.Session.run for details of the allowable feed key and value types.

The returned callable will have the same return type as tf.Session.run(fetches, ...). For example, if fetches is a tf.Tensor, the callable will return a numpy ndarray; if fetches is a tf.Operation, it will return None.

Args
fetches	A value or list of values to fetch. See tf.Session.run for details of the allowable fetch types.
feed_list	(Optional.) A list of feed_dict keys. See tf.Session.run for details of the allowable feed key types.
accept_options	(Optional.) If True, the returned Callable will be able to accept tf.compat.v1.RunOptions and tf.compat.v1.RunMetadata as optional keyword arguments options and run_metadata, respectively, with the same syntax and semantics as tf.Session.run, which is useful for certain use cases (profiling and debugging) but will result in measurable slowdown of the Callable's performance. Default: False.

Returns
A function that when called will execute the step defined by feed_list and fetches in this session.

Raises
TypeError	If fetches or feed_list cannot be interpreted as arguments to tf.Session.run.

partial_run

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partial_run(
    handle, fetches, feed_dict=None
)

Continues the execution with more feeds and fetches.

This is EXPERIMENTAL and subject to change.

To use partial execution, a user first calls partial_run_setup() and then a sequence of partial_run(). partial_run_setup specifies the list of feeds and fetches that will be used in the subsequent partial_run calls.

The optional feed_dict argument allows the caller to override the value of tensors in the graph. See run() for more information.

Below is a simple example:

a = array_ops.placeholder(dtypes.float32, shape=[])
b = array_ops.placeholder(dtypes.float32, shape=[])
c = array_ops.placeholder(dtypes.float32, shape=[])
r1 = math_ops.add(a, b)
r2 = math_ops.multiply(r1, c)

h = sess.partial_run_setup([r1, r2], [a, b, c])
res = sess.partial_run(h, r1, feed_dict={a: 1, b: 2})
res = sess.partial_run(h, r2, feed_dict={c: res})

Args
handle	A handle for a sequence of partial runs.
fetches	A single graph element, a list of graph elements, or a dictionary whose values are graph elements or lists of graph elements (see documentation for run).
feed_dict	A dictionary that maps graph elements to values (described above).

Returns
Either a single value if fetches is a single graph element, or a list of values if fetches is a list, or a dictionary with the same keys as fetches if that is a dictionary (see documentation for run).

Raises
tf.errors.OpError	Or one of its subclasses on error.

partial_run_setup

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partial_run_setup(
    fetches, feeds=None
)

Sets up a graph with feeds and fetches for partial run.

This is EXPERIMENTAL and subject to change.

Note that contrary to run, feeds only specifies the graph elements. The tensors will be supplied by the subsequent partial_run calls.

Args
fetches	A single graph element, or a list of graph elements.
feeds	A single graph element, or a list of graph elements.

Returns
A handle for partial run.

Raises
RuntimeError	If this Session is in an invalid state (e.g. has been closed).
TypeError	If fetches or feed_dict keys are of an inappropriate type.
tf.errors.OpError	Or one of its subclasses if a TensorFlow error happens.

reset

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@staticmethod
reset(
    target, containers=None, config=None
)

Resets resource containers on target, and close all connected sessions.

A resource container is distributed across all workers in the same cluster as target. When a resource container on target is reset, resources associated with that container will be cleared. In particular, all Variables in the container will become undefined: they lose their values and shapes.

NOTE:

(i) reset() is currently only implemented for distributed sessions. (ii) Any sessions on the master named by target will be closed.

If no resource containers are provided, all containers are reset.

Args
target	The execution engine to connect to.
containers	A list of resource container name strings, or None if all of all the containers are to be reset.
config	(Optional.) Protocol buffer with configuration options.

Raises
tf.errors.OpError	Or one of its subclasses if an error occurs while resetting containers.

run

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run(
    fetches, feed_dict=None, options=None, run_metadata=None
)

Runs operations and evaluates tensors in fetches.

This method runs one "step" of TensorFlow computation, by running the necessary graph fragment to execute every Operation and evaluate every Tensor in fetches, substituting the values in feed_dict for the corresponding input values.

The fetches argument may be a single graph element, or an arbitrarily nested list, tuple, namedtuple, dict, or OrderedDict containing graph elements at its leaves. A graph element can be one of the following types:

• A tf.Operation. The corresponding fetched value will be None.
• A tf.Tensor. The corresponding fetched value will be a numpy ndarray containing the value of that tensor.
• A tf.SparseTensor. The corresponding fetched value will be a tf.compat.v1.SparseTensorValue containing the value of that sparse tensor.
• A get_tensor_handle op. The corresponding fetched value will be a numpy ndarray containing the handle of that tensor.
• A string which is the name of a tensor or operation in the graph.

The value returned by run() has the same shape as the fetches argument, where the leaves are replaced by the corresponding values returned by TensorFlow.

Example:

a = tf.constant([10, 20])
b = tf.constant([1.0, 2.0])
# 'fetches' can be a singleton
v = session.run(a)
# v is the numpy array [10, 20]
# 'fetches' can be a list.
v = session.run([a, b])
# v is a Python list with 2 numpy arrays: the 1-D array [10, 20] and the
# 1-D array [1.0, 2.0]
# 'fetches' can be arbitrary lists, tuples, namedtuple, dicts:
MyData = collections.namedtuple('MyData', ['a', 'b'])
v = session.run({'k1': MyData(a, b), 'k2': [b, a]})
# v is a dict with
# v['k1'] is a MyData namedtuple with 'a' (the numpy array [10, 20]) and
# 'b' (the numpy array [1.0, 2.0])
# v['k2'] is a list with the numpy array [1.0, 2.0] and the numpy array
# [10, 20].

The optional feed_dict argument allows the caller to override the value of tensors in the graph. Each key in feed_dict can be one of the following types:

• If the key is a tf.Tensor, the value may be a Python scalar, string, list, or numpy ndarray that can be converted to the same dtype as that tensor. Additionally, if the key is a tf.compat.v1.placeholder, the shape of the value will be checked for compatibility with the placeholder.
• If the key is a tf.SparseTensor, the value should be a tf.compat.v1.SparseTensorValue.
• If the key is a nested tuple of Tensors or SparseTensors, the value should be a nested tuple with the same structure that maps to their corresponding values as above.

Each value in feed_dict must be convertible to a numpy array of the dtype of the corresponding key.

The optional options argument expects a [RunOptions] proto. The options allow controlling the behavior of this particular step (e.g. turning tracing on).

The optional run_metadata argument expects a [RunMetadata] proto. When appropriate, the non-Tensor output of this step will be collected there. For example, when users turn on tracing in options, the profiled info will be collected into this argument and passed back.

Args
fetches	A single graph element, a list of graph elements, or a dictionary whose values are graph elements or lists of graph elements (described above).
feed_dict	A dictionary that maps graph elements to values (described above).
options	A [RunOptions] protocol buffer
run_metadata	A [RunMetadata] protocol buffer

Returns
Either a single value if fetches is a single graph element, or a list of values if fetches is a list, or a dictionary with the same keys as fetches if that is a dictionary (described above). Order in which fetches operations are evaluated inside the call is undefined.

Raises
RuntimeError	If this Session is in an invalid state (e.g. has been closed).
TypeError	If fetches or feed_dict keys are of an inappropriate type.
ValueError	If fetches or feed_dict keys are invalid or refer to a Tensor that doesn't exist.

__enter__

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__enter__()

__exit__

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__exit__(
    exec_type, exec_value, exec_tb
)