:mod:`email.generator`: Generating MIME documents

.. module:: email.generator :synopsis: Generate flat text email messages from a message structure.

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

One of the most common tasks is to generate the flat (serialized) version of the email message represented by a message object structure. You will need to do this if you want to send your message via :meth:smtplib.SMTP.sendmail or the :mod:nntplib module, or print the message on the console. Taking a message object structure and producing a serialized representation is the job of the generator classes.

As with the :mod:email.parser module, you aren't limited to the functionality of the bundled generator; you could write one from scratch yourself. However the bundled generator knows how to generate most email in a standards-compliant way, should handle MIME and non-MIME email messages just fine, and is designed so that the bytes-oriented parsing and generation operations are inverses, assuming the same non-transforming :mod:~email.policy is used for both. That is, parsing the serialized byte stream via the :class:~email.parser.BytesParser class and then regenerating the serialized byte stream using :class:BytesGenerator should produce output identical to the input [#]_. (On the other hand, using the generator on an :class:~email.message.EmailMessage constructed by program may result in changes to the :class:~email.message.EmailMessage object as defaults are filled in.)

The :class:Generator class can be used to flatten a message into a text (as opposed to binary) serialized representation, but since Unicode cannot represent binary data directly, the message is of necessity transformed into something that contains only ASCII characters, using the standard email RFC Content Transfer Encoding techniques for encoding email messages for transport over channels that are not "8 bit clean".

.. class:: BytesGenerator(outfp, mangle_from_=None, maxheaderlen=None, *,
policy=None)

Return a :class:BytesGenerator object that will write any message provided to the :meth:flatten method, or any surrogateescape encoded text provided to the :meth:write method, to the :term:file-like object outfp. outfp must support a write method that accepts binary data.

If optional mangle_from_ is True, put a > character in front of any line in the body that starts with the exact string "From ", that is From followed by a space at the beginning of a line. mangle_from_ defaults to the value of the :attr:~email.policy.Policy.mangle_from_ setting of the policy (which is True for the :data:~email.policy.compat32 policy and False for all others). mangle_from_ is intended for use when messages are stored in unix mbox format (see :mod:mailbox and WHY THE CONTENT-LENGTH FORMAT IS BAD <https://www.jwz.org/doc/content-length.html>_).

If maxheaderlen is not None, refold any header lines that are longer than maxheaderlen, or if 0, do not rewrap any headers. If manheaderlen is None (the default), wrap headers and other message lines according to the policy settings.

If policy is specified, use that policy to control message generation. If policy is None (the default), use the policy associated with the :class:~email.message.Message or :class:~email.message.EmailMessage object passed to flatten to control the message generation. See :mod:email.policy for details on what policy controls.

.. versionadded:: 3.2

.. versionchanged:: 3.3 Added the policy keyword.

.. versionchanged:: 3.6 The default behavior of the mangle_from_ and maxheaderlen parameters is to follow the policy.

.. method:: flatten(msg, unixfrom=False, linesep=None)

  Print the textual representation of the message object structure rooted
  at *msg* to the output file specified when the :class:`BytesGenerator`
  instance was created.

  If the :mod:`~email.policy` option :attr:`~email.policy.Policy.cte_type`
  is ``8bit`` (the default), copy any headers in the original parsed
  message that have not been modified to the output with any bytes with the
  high bit set reproduced as in the original, and preserve the non-ASCII
  :mailheader:`Content-Transfer-Encoding` of any body parts that have them.
  If ``cte_type`` is ``7bit``, convert the bytes with the high bit set as
  needed using an ASCII-compatible :mailheader:`Content-Transfer-Encoding`.
  That is, transform parts with non-ASCII
  :mailheader:`Content-Transfer-Encoding`
  (:mailheader:`Content-Transfer-Encoding: 8bit`) to an ASCII compatible
  :mailheader:`Content-Transfer-Encoding`, and encode RFC-invalid non-ASCII
  bytes in headers using the MIME ``unknown-8bit`` character set, thus
  rendering them RFC-compliant.

  .. XXX: There should be an option that just does the RFC
     compliance transformation on headers but leaves CTE 8bit parts alone.

  If *unixfrom* is ``True``, print the envelope header delimiter used by
  the Unix mailbox format (see :mod:`mailbox`) before the first of the
  :rfc:`5322` headers of the root message object.  If the root object has
  no envelope header, craft a standard one.  The default is ``False``.
  Note that for subparts, no envelope header is ever printed.

  If *linesep* is not ``None``, use it as the separator character between
  all the lines of the flattened message.  If *linesep* is ``None`` (the
  default), use the value specified in the *policy*.

  .. XXX: flatten should take a *policy* keyword.

.. method:: clone(fp)

  Return an independent clone of this :class:`BytesGenerator` instance with
  the exact same option settings, and *fp* as the new *outfp*.

.. method:: write(s)

  Encode *s* using the ``ASCII`` codec and the ``surrogateescape`` error
  handler, and pass it to the *write* method of the *outfp* passed to the
  :class:`BytesGenerator`'s constructor.

As a convenience, :class:~email.message.EmailMessage provides the methods :meth:~email.message.EmailMessage.as_bytes and bytes(aMessage) (a.k.a. :meth:~email.message.EmailMessage.__bytes__), which simplify the generation of a serialized binary representation of a message object. For more detail, see :mod:email.message.

Because strings cannot represent binary data, the :class:Generator class must convert any binary data in any message it flattens to an ASCII compatible format, by converting them to an ASCII compatible :mailheader:Content-Transfer_Encoding. Using the terminology of the email RFCs, you can think of this as :class:Generator serializing to an I/O stream that is not "8 bit clean". In other words, most applications will want to be using :class:BytesGenerator, and not :class:Generator.

.. class:: Generator(outfp, mangle_from_=None, maxheaderlen=None, *,
policy=None)

Return a :class:Generator object that will write any message provided to the :meth:flatten method, or any text provided to the :meth:write method, to the :term:file-like object outfp. outfp must support a write method that accepts string data.

.. versionchanged:: 3.3 Added the policy keyword.

.. versionchanged:: 3.6 The default behavior of the mangle_from_ and maxheaderlen parameters is to follow the policy.

.. method:: flatten(msg, unixfrom=False, linesep=None)

  Print the textual representation of the message object structure rooted
  at *msg* to the output file specified when the :class:`Generator`
  instance was created.

  If the :mod:`~email.policy` option :attr:`~email.policy.Policy.cte_type`
  is ``8bit``, generate the message as if the option were set to ``7bit``.
  (This is required because strings cannot represent non-ASCII bytes.)
  Convert any bytes with the high bit set as needed using an
  ASCII-compatible :mailheader:`Content-Transfer-Encoding`.  That is,
  transform parts with non-ASCII :mailheader:`Cotnent-Transfer-Encoding`
  (:mailheader:`Content-Transfer-Encoding: 8bit`) to an ASCII compatible
  :mailheader:`Content-Transfer-Encoding`, and encode RFC-invalid non-ASCII
  bytes in headers using the MIME ``unknown-8bit`` character set, thus
  rendering them RFC-compliant.

  If *unixfrom* is ``True``, print the envelope header delimiter used by
  the Unix mailbox format (see :mod:`mailbox`) before the first of the
  :rfc:`5322` headers of the root message object.  If the root object has
  no envelope header, craft a standard one.  The default is ``False``.
  Note that for subparts, no envelope header is ever printed.

  If *linesep* is not ``None``, use it as the separator character between
  all the lines of the flattened message.  If *linesep* is ``None`` (the
  default), use the value specified in the *policy*.

  .. XXX: flatten should take a *policy* keyword.

  .. versionchanged:: 3.2
     Added support for re-encoding ``8bit`` message bodies, and the
     *linesep* argument.

.. method:: clone(fp)

  Return an independent clone of this :class:`Generator` instance with the
  exact same options, and *fp* as the new *outfp*.

.. method:: write(s)

  Write *s* to the *write* method of the *outfp* passed to the
  :class:`Generator`'s constructor.  This provides just enough file-like
  API for :class:`Generator` instances to be used in the :func:`print`
  function.

As a convenience, :class:~email.message.EmailMessage provides the methods :meth:~email.message.EmailMessage.as_string and str(aMessage) (a.k.a. :meth:~email.message.EmailMessage.__str__), which simplify the generation of a formatted string representation of a message object. For more detail, see :mod:email.message.

The :mod:email.generator module also provides a derived class, :class:DecodedGenerator, which is like the :class:Generator base class, except that non-\ :mimetype:text parts are not serialized, but are instead represented in the output stream by a string derived from a template filled in with information about the part.

.. class:: DecodedGenerator(outfp, mangle_from_=None, maxheaderlen=None,
fmt=None, *, policy=None)

Act like :class:Generator, except that for any subpart of the message passed to :meth:Generator.flatten, if the subpart is of main type :mimetype:text, print the decoded payload of the subpart, and if the main type is not :mimetype:text, instead of printing it fill in the string fmt using information from the part and print the resulting filled-in string.

To fill in fmt, execute fmt % part_info, where part_info is a dictionary composed of the following keys and values:

type -- Full MIME type of the non-\ :mimetype:text part
maintype -- Main MIME type of the non-\ :mimetype:text part
subtype -- Sub-MIME type of the non-\ :mimetype:text part
filename -- Filename of the non-\ :mimetype:text part
description -- Description associated with the non-\ :mimetype:text part
encoding -- Content transfer encoding of the non-\ :mimetype:text part

If fmt is None, use the following default fmt:

  "[Non-text (%(type)s) part of message omitted, filename %(filename)s]"

Optional mangle_from and maxheaderlen are as with the :class:Generator base class.

.. rubric:: Footnotes

.. [#] This statement assumes that you use the appropriate setting for unixfrom, and that there are no :mod:policy settings calling for automatic adjustments (for example, :attr:~email.policy.Policy.refold_source must be none, which is not the default). It is also not 100% true, since if the message does not conform to the RFC standards occasionally information about the exact original text is lost during parsing error recovery. It is a goal to fix these latter edge cases when possible.

:mod:`email.generator`: Generating MIME documents

:mod:email.generator: Generating MIME documents

:mod:`email.generator`: Generating MIME documents