:mod:`email`: Generating MIME documents

---------------------------------------

.. module:: email.generator

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

One of the most common tasks is to generate the flat text of the email message

represented by a message object structure.  You will need to do this if you want

to send your message via the :mod:`smtplib` module or the :mod:`nntplib` module,

or print the message on the console.  Taking a message object structure and

producing a flat text document is the job of the :class:`Generator` class.

Again, 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 transformation from flat text, to a message

structure via the :class:`Parser` class, and back to flat text, is idempotent

(the input is identical to the output).

Here are the public methods of the :class:`Generator` class, imported from the

:mod:`email.generator` module:

.. class:: Generator(outfp[, mangle_from_[, maxheaderlen]])

   The constructor for the :class:`Generator` class takes a file-like object called

   *outfp* for an argument.  *outfp* must support the :meth:`write` method and be

   usable as the output file in a Python extended print statement.

   Optional *mangle_from_* is a flag that, when ``True``, puts a ``>`` character in

   front of any line in the body that starts exactly as ``From``, i.e. ``From``

   followed by a space at the beginning of the line.  This is the only guaranteed

   portable way to avoid having such lines be mistaken for a Unix mailbox format

   envelope header separator (see `WHY THE CONTENT-LENGTH FORMAT IS BAD

   <http://www.jwz.org/doc/content-length.html>`_ for details).  *mangle_from_*

   defaults to ``True``, but you might want to set this to ``False`` if you are not

   writing Unix mailbox format files.

   Optional *maxheaderlen* specifies the longest length for a non-continued header.

   When a header line is longer than *maxheaderlen* (in characters, with tabs

   expanded to 8 spaces), the header will be split as defined in the

   :mod:`email.header.Header` class.  Set to zero to disable header wrapping.  The

   default is 78, as recommended (but not required) by :rfc:`2822`.

   The other public :class:`Generator` methods are:

   .. method:: flatten(msg[, unixfrom])

      Print the textual representation of the message object structure rooted at

      *msg* to the output file specified when the :class:`Generator` instance

      was created.  Subparts are visited depth-first and the resulting text will

      be properly MIME encoded.

      Optional *unixfrom* is a flag that forces the printing of the envelope

      header delimiter before the first :rfc:`2822` header of the root message

      object.  If the root object has no envelope header, a standard one is

      crafted.  By default, this is set to ``False`` to inhibit the printing of

      the envelope delimiter.

      Note that for subparts, no envelope header is ever printed.

      .. versionadded:: 2.2.2

   .. method:: clone(fp)

      Return an independent clone of this :class:`Generator` instance with the

      exact same options.

      .. versionadded:: 2.2.2

   .. method:: write(s)

      Write the string *s* to the underlying file object, i.e. *outfp* passed to

      :class:`Generator`'s constructor.  This provides just enough file-like API

      for :class:`Generator` instances to be used in extended print statements.

As a convenience, see the methods :meth:`Message.as_string` and

``str(aMessage)``, a.k.a. :meth:`Message.__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, called

:class:`DecodedGenerator` which is like the :class:`Generator` base class,

except that non-\ :mimetype:`text` parts are substituted with a format string

representing the part.

.. class:: DecodedGenerator(outfp[, mangle_from_[, maxheaderlen[, fmt]]])

   This class, derived from :class:`Generator` walks through all the subparts of a

   message.  If the subpart is of main type :mimetype:`text`, then it prints the

   decoded payload of the subpart. Optional *_mangle_from_* and *maxheaderlen* are

   as with the :class:`Generator` base class.

   If the subpart is not of main type :mimetype:`text`, optional *fmt* is a format

   string that is used instead of the message payload. *fmt* is expanded with the

   following keywords, ``%(keyword)s`` format:

   * ``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

   The default value for *fmt* is ``None``, meaning ::

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

   .. versionadded:: 2.2.2

.. versionchanged:: 2.5

   The previously deprecated method :meth:`__call__` was removed.