Source code: Lib/email/__init__.py
The overall structure of the email package can be divided into three major components, plus a fourth component that controls the behavior of the other components.
The central component of the package is an “object model” that represents email messages. An application interacts with the package primarily through the object model interface defined in the
message sub-module. The application can use this API to ask questions about an existing email, to construct a new email, or to add or remove email subcomponents that themselves use the same object model interface. That is, following the nature of email messages and their MIME subcomponents, the email object model is a tree structure of objects that all provide the
The other two major components of the package are the
parser and the
generator. The parser takes the serialized version of an email message (a stream of bytes) and converts it into a tree of
EmailMessage objects. The generator takes an
EmailMessage and turns it back into a serialized byte stream. (The parser and generator also handle streams of text characters, but this usage is discouraged as it is too easy to end up with messages that are not valid in one way or another.)
The control component is the
policy module. Every
generator, and every
parser has an associated
policy object that controls its behavior. Usually an application only needs to specify the policy when an
EmailMessage is created, either by directly instantiating an
EmailMessage to create a new email, or by parsing an input stream using a
parser. But the policy can be changed when the message is serialized using a
generator. This allows, for example, a generic email message to be parsed from disk, but to serialize it using standard SMTP settings when sending it to an email server.
The email package does its best to hide the details of the various governing RFCs from the application. Conceptually the application should be able to treat the email message as a structured tree of unicode text and binary attachments, without having to worry about how these are represented when serialized. In practice, however, it is often necessary to be aware of at least some of the rules governing MIME messages and their structure, specifically the names and nature of the MIME “content types” and how they identify multipart documents. For the most part this knowledge should only be required for more complex applications, and even then it should only be the high level structure in question, and not the details of how those structures are represented. Since MIME content types are used widely in modern internet software (not just email), this will be a familiar concept to many programmers.
The following sections describe the functionality of the
message object model, which is the primary interface an application will use, and follow that with the
generator components. Then we cover the
policy controls, which completes the treatment of the main components of the library.
The next three sections cover the exceptions the package may raise and the defects (non-compliance with the RFCs) that the
parser may detect. Then we cover the
headerregistry and the
contentmanager sub-components, which provide tools for doing more detailed manipulation of headers and payloads, respectively. Both of these components contain features relevant to consuming and producing non-trivial messages, but also document their extensibility APIs, which will be of interest to advanced applications.
Following those is a set of examples of using the fundamental parts of the APIs covered in the preceding sections.
The forgoing represent the modern (unicode friendly) API of the email package. The remaining sections, starting with the
Message class, cover the legacy
compat32 API that deals much more directly with the details of how email messages are represented. The
compat32 API does not hide the details of the RFCs from the application, but for applications that need to operate at that level, they can be useful tools. This documentation is also relevant for applications that are still using the
compat32 API for backward compatibility reasons.
Contents of the
email.message: Representing an email message
email.parser: Parsing email messages
email.generator: Generating MIME documents
email.policy: Policy Objects
email.errors: Exception and Defect classes
email.headerregistry: Custom Header Objects
email.contentmanager: Managing MIME Content
email.message.Message: Representing an email message using the
email.mime: Creating email and MIME objects from scratch
email.header: Internationalized headers
email.charset: Representing character sets
email.utils: Miscellaneous utilities
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