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:mod:`email.parser`: Parsing email messages

kbe/src/lib/python/Doc/library/email.parser.rst

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:mod:email.parser: Parsing email messages

.. module:: email.parser :synopsis: Parse flat text email messages to produce a message object structure.

Source code: :source:Lib/email/parser.py

Message object structures can be created in one of two ways: they can be created from whole cloth by creating an :class:~email.message.EmailMessage object, adding headers using the dictionary interface, and adding payload(s) using :meth:~email.message.EmailMessage.set_content and related methods, or they can be created by parsing a serialized representation of the email message.

The :mod:email package provides a standard parser that understands most email document structures, including MIME documents. You can pass the parser a bytes, string or file object, and the parser will return to you the root :class:~email.message.EmailMessage instance of the object structure. For simple, non-MIME messages the payload of this root object will likely be a string containing the text of the message. For MIME messages, the root object will return True from its :meth:~email.message.EmailMessage.is_multipart method, and the subparts can be accessed via the payload manipulation methods, such as :meth:~email.message.EmailMessage.get_body, :meth:~email.message.EmailMessage.iter_parts, and :meth:~email.message.EmailMessage.walk.

There are actually two parser interfaces available for use, the :class:Parser API and the incremental :class:FeedParser API. The :class:Parser API is most useful if you have the entire text of the message in memory, or if the entire message lives in a file on the file system. :class:FeedParser is more appropriate when you are reading the message from a stream which might block waiting for more input (such as reading an email message from a socket). The :class:FeedParser can consume and parse the message incrementally, and only returns the root object when you close the parser.

Note that the parser can be extended in limited ways, and of course you can implement your own parser completely from scratch. All of the logic that connects the :mod:email package's bundled parser and the :class:~email.message.EmailMessage class is embodied in the :mod:policy class, so a custom parser can create message object trees any way it finds necessary by implementing custom versions of the appropriate :mod:policy methods.

FeedParser API ^^^^^^^^^^^^^^

The :class:BytesFeedParser, imported from the :mod:email.feedparser module, provides an API that is conducive to incremental parsing of email messages, such as would be necessary when reading the text of an email message from a source that can block (such as a socket). The :class:BytesFeedParser can of course be used to parse an email message fully contained in a :term:bytes-like object, string, or file, but the :class:BytesParser API may be more convenient for such use cases. The semantics and results of the two parser APIs are identical.

The :class:BytesFeedParser's API is simple; you create an instance, feed it a bunch of bytes until there's no more to feed it, then close the parser to retrieve the root message object. The :class:BytesFeedParser is extremely accurate when parsing standards-compliant messages, and it does a very good job of parsing non-compliant messages, providing information about how a message was deemed broken. It will populate a message object's :attr:~email.message.EmailMessage.defects attribute with a list of any problems it found in a message. See the :mod:email.errors module for the list of defects that it can find.

Here is the API for the :class:BytesFeedParser:

.. class:: BytesFeedParser(_factory=None, *, policy=policy.compat32)

Create a :class:BytesFeedParser instance. Optional _factory is a no-argument callable; if not specified use the :attr:~email.policy.Policy.message_factory from the policy. Call _factory whenever a new message object is needed.

If policy is specified use the rules it specifies to update the representation of the message. If policy is not set, use the :class:compat32 <email.policy.Compat32> policy, which maintains backward compatibility with the Python 3.2 version of the email package and provides :class:~email.message.Message as the default factory. All other policies provide :class:~email.message.EmailMessage as the default _factory. For more information on what else policy controls, see the :mod:~email.policy documentation.

Note: The policy keyword should always be specified; The default will change to :data:email.policy.default in a future version of Python.

.. versionadded:: 3.2

.. versionchanged:: 3.3 Added the policy keyword. .. versionchanged:: 3.6 _factory defaults to the policy message_factory.

.. method:: feed(data)

  Feed the parser some more data.  *data* should be a :term:`bytes-like
  object` containing one or more lines.  The lines can be partial and the
  parser will stitch such partial lines together properly.  The lines can
  have any of the three common line endings: carriage return, newline, or
  carriage return and newline (they can even be mixed).

.. method:: close()

  Complete the parsing of all previously fed data and return the root
  message object.  It is undefined what happens if :meth:`~feed` is called
  after this method has been called.

.. class:: FeedParser(_factory=None, *, policy=policy.compat32)

Works like :class:BytesFeedParser except that the input to the :meth:~BytesFeedParser.feed method must be a string. This is of limited utility, since the only way for such a message to be valid is for it to contain only ASCII text or, if :attr:~email.policy.Policy.utf8 is True, no binary attachments.

.. versionchanged:: 3.3 Added the policy keyword.

Parser API ^^^^^^^^^^

The :class:BytesParser class, imported from the :mod:email.parser module, provides an API that can be used to parse a message when the complete contents of the message are available in a :term:bytes-like object or file. The :mod:email.parser module also provides :class:Parser for parsing strings, and header-only parsers, :class:BytesHeaderParser and :class:HeaderParser, which can be used if you're only interested in the headers of the message. :class:BytesHeaderParser and :class:HeaderParser can be much faster in these situations, since they do not attempt to parse the message body, instead setting the payload to the raw body.

.. class:: BytesParser(_class=None, *, policy=policy.compat32)

Create a :class:BytesParser instance. The _class and policy arguments have the same meaning and semantics as the _factory and policy arguments of :class:BytesFeedParser.

Note: The policy keyword should always be specified; The default will change to :data:email.policy.default in a future version of Python.

.. versionchanged:: 3.3 Removed the strict argument that was deprecated in 2.4. Added the policy keyword. .. versionchanged:: 3.6 _class defaults to the policy message_factory.

.. method:: parse(fp, headersonly=False)

  Read all the data from the binary file-like object *fp*, parse the
  resulting bytes, and return the message object.  *fp* must support
  both the :meth:`~io.IOBase.readline` and the :meth:`~io.IOBase.read`
  methods.

  The bytes contained in *fp* must be formatted as a block of :rfc:`5322`
  (or, if :attr:`~email.policy.Policy.utf8` is ``True``, :rfc:`6532`)
  style headers and header continuation lines, optionally preceded by an
  envelope header.  The header block is terminated either by the end of the
  data or by a blank line.  Following the header block is the body of the
  message (which may contain MIME-encoded subparts, including subparts
  with a :mailheader:`Content-Transfer-Encoding` of ``8bit``).

  Optional *headersonly* is a flag specifying whether to stop parsing after
  reading the headers or not.  The default is ``False``, meaning it parses
  the entire contents of the file.

.. method:: parsebytes(bytes, headersonly=False)

  Similar to the :meth:`parse` method, except it takes a :term:`bytes-like
  object` instead of a file-like object.  Calling this method on a
  :term:`bytes-like object` is equivalent to wrapping *bytes* in a
  :class:`~io.BytesIO` instance first and calling :meth:`parse`.

  Optional *headersonly* is as with the :meth:`parse` method.

.. versionadded:: 3.2

.. class:: BytesHeaderParser(_class=None, *, policy=policy.compat32)

Exactly like :class:BytesParser, except that headersonly defaults to True.

.. versionadded:: 3.3

.. class:: Parser(_class=None, *, policy=policy.compat32)

This class is parallel to :class:BytesParser, but handles string input.

.. versionchanged:: 3.3 Removed the strict argument. Added the policy keyword. .. versionchanged:: 3.6 _class defaults to the policy message_factory.

.. method:: parse(fp, headersonly=False)

  Read all the data from the text-mode file-like object *fp*, parse the
  resulting text, and return the root message object.  *fp* must support
  both the :meth:`~io.TextIOBase.readline` and the
  :meth:`~io.TextIOBase.read` methods on file-like objects.

  Other than the text mode requirement, this method operates like
  :meth:`BytesParser.parse`.

.. method:: parsestr(text, headersonly=False)

  Similar to the :meth:`parse` method, except it takes a string object
  instead of a file-like object.  Calling this method on a string is
  equivalent to wrapping *text* in a :class:`~io.StringIO` instance first
  and calling :meth:`parse`.

  Optional *headersonly* is as with the :meth:`parse` method.

.. class:: HeaderParser(_class=None, *, policy=policy.compat32)

Exactly like :class:Parser, except that headersonly defaults to True.

Since creating a message object structure from a string or a file object is such a common task, four functions are provided as a convenience. They are available in the top-level :mod:email package namespace.

.. currentmodule:: email

.. function:: message_from_bytes(s, _class=None, *, policy=policy.compat32)

Return a message object structure from a :term:bytes-like object. This is equivalent to BytesParser().parsebytes(s). Optional _class and policy are interpreted as with the :class:~email.parser.BytesParser class constructor.

.. versionadded:: 3.2 .. versionchanged:: 3.3 Removed the strict argument. Added the policy keyword.

.. function:: message_from_binary_file(fp, _class=None, *,
policy=policy.compat32)

Return a message object structure tree from an open binary :term:file object. This is equivalent to BytesParser().parse(fp). _class and policy are interpreted as with the :class:~email.parser.BytesParser class constructor.

.. versionadded:: 3.2 .. versionchanged:: 3.3 Removed the strict argument. Added the policy keyword.

.. function:: message_from_string(s, _class=None, *, policy=policy.compat32)

Return a message object structure from a string. This is equivalent to Parser().parsestr(s). _class and policy are interpreted as with the :class:~email.parser.Parser class constructor.

.. versionchanged:: 3.3 Removed the strict argument. Added the policy keyword.

.. function:: message_from_file(fp, _class=None, *, policy=policy.compat32)

Return a message object structure tree from an open :term:file object. This is equivalent to Parser().parse(fp). _class and policy are interpreted as with the :class:~email.parser.Parser class constructor.

.. versionchanged:: 3.3 Removed the strict argument. Added the policy keyword. .. versionchanged:: 3.6 _class defaults to the policy message_factory.

Here's an example of how you might use :func:message_from_bytes at an interactive Python prompt::

import email msg = email.message_from_bytes(myBytes) # doctest: +SKIP

Additional notes ^^^^^^^^^^^^^^^^

Here are some notes on the parsing semantics:

  • Most non-\ :mimetype:multipart type messages are parsed as a single message object with a string payload. These objects will return False for :meth:~email.message.EmailMessage.is_multipart, and :meth:~email.message.EmailMessage.iter_parts will yield an empty list.

  • All :mimetype:multipart type messages will be parsed as a container message object with a list of sub-message objects for their payload. The outer container message will return True for :meth:~email.message.EmailMessage.is_multipart, and :meth:~email.message.EmailMessage.iter_parts will yield a list of subparts.

  • Most messages with a content type of :mimetype:message/\* (such as :mimetype:message/delivery-status and :mimetype:message/rfc822) will also be parsed as container object containing a list payload of length 1. Their :meth:~email.message.EmailMessage.is_multipart method will return True. The single element yielded by :meth:~email.message.EmailMessage.iter_parts will be a sub-message object.

  • Some non-standards-compliant messages may not be internally consistent about their :mimetype:multipart\ -edness. Such messages may have a :mailheader:Content-Type header of type :mimetype:multipart, but their :meth:~email.message.EmailMessage.is_multipart method may return False. If such messages were parsed with the :class:~email.parser.FeedParser, they will have an instance of the :class:~email.errors.MultipartInvariantViolationDefect class in their defects attribute list. See :mod:email.errors for details.