2 ._I|Mjq؂ai~ *j"TfţFile not found. "li~ *j"Tfţ hacpi:LNXPWRBN:  hon " lad*j"Tځz@ؔţ }%Y :mod:`email` Package Architecture ================================= Overview -------- The email package consists of three major components: Model An object structure that represents an email message, and provides an API for creating, querying, and modifying a message. Parser Takes a sequence of characters or bytes and produces a model of the email message represented by those characters or bytes. Generator Takes a model and turns it into a sequence of characters or bytes. The sequence can either be intended for human consumption (a printable unicode string) or bytes suitable for transmission over the wire. In the latter case all data is properly encoded using the content transfer encodings specified by the relevant RFCs. Conceptually the package is organized around the model. The model provides both "external" APIs intended for use by application programs using the library, and "internal" APIs intended for use by the Parser and Generator components. This division is intentionally a bit fuzzy; the API described by this documentation is all a public, stable API. This allows for an application with special needs to implement its own parser and/or generator. In addition to the three major functional components, there is a third key component to the architecture: Policy An object that specifies various behavioral settings and carries implementations of various behavior-controlling methods. The Policy framework provides a simple and convenient way to control the behavior of the library, making it possible for the library to be used in a very flexible fashion while leveraging the common code required to parse, represent, and generate message-like objects. For example, in addition to the default :rfc:`5322` email message policy, we also have a policy that manages HTTP headers in a fashion compliant with :rfc:`2616`. Individual policy controls, such as the maximum line length produced by the generator, can also be controlled individually to meet specialized application requirements. The Model --------- The message model is implemented by the :class:`~email.message.Message` class. The model divides a message into the two fundamental parts discussed by the RFC: the header section and the body. The `Message` object acts as a pseudo-dictionary of named headers. Its dictionary interface provides convenient access to individual headers by name. However, all headers are kept internally in an ordered list, so that the information about the order of the headers in the original message is preserved. The `Message` object also has a `payload` that holds the body. A `payload` can be one of two things: data, or a list of `Message` objects. The latter is used to represent a multipart MIME message. Lists can be nested arbitrarily deeply in order to represent the message, with all terminal leaves having non-list data payloads. Message Lifecycle ----------------- The general lifecycle of a message is: Creation A `Message` object can be created by a Parser, or it can be instantiated as an empty message by an application. Manipulation The application may examine one or more headers, and/or the payload, and it may modify one or more headers and/or the payload. This may be done on the top level `Message` object, or on any sub-object. Finalization The Model is converted into a unicode or binary stream, or the model is discarded. Header Policy Control During Lifecycle -------------------------------------- One of the major controls exerted by the Policy is the management of headers during the `Message` lifecycle. Most applications don't need to be aware of this. A header enters the model in one of two ways: via