xref: /third_party/python/Doc/library/email.contentmanager.rst

:mod:`email.contentmanager`: Managing MIME Content
--------------------------------------------------

.. module:: email.contentmanager
   :synopsis: Storing and Retrieving Content from MIME Parts

.. moduleauthor:: R. David Murray <rdmurray@bitdance.com>
.. sectionauthor:: R. David Murray <rdmurray@bitdance.com>

**Source code:** :source:`Lib/email/contentmanager.py`

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

.. versionadded:: 3.6 [1]_


.. class:: ContentManager()

   Base class for content managers.  Provides the standard registry mechanisms
   to register converters between MIME content and other representations, as
   well as the ``get_content`` and ``set_content`` dispatch methods.


   .. method:: get_content(msg, *args, **kw)

      Look up a handler function based on the ``mimetype`` of *msg* (see next
      paragraph), call it, passing through all arguments, and return the result
      of the call.  The expectation is that the handler will extract the
      payload from *msg* and return an object that encodes information about
      the extracted data.

      To find the handler, look for the following keys in the registry,
      stopping with the first one found:

            * the string representing the full MIME type (``maintype/subtype``)
            * the string representing the ``maintype``
            * the empty string

      If none of these keys produce a handler, raise a :exc:`KeyError` for the
      full MIME type.


   .. method:: set_content(msg, obj, *args, **kw)

      If the ``maintype`` is ``multipart``, raise a :exc:`TypeError`; otherwise
      look up a handler function based on the type of *obj* (see next
      paragraph), call :meth:`~email.message.EmailMessage.clear_content` on the
      *msg*, and call the handler function, passing through all arguments.  The
      expectation is that the handler will transform and store *obj* into
      *msg*, possibly making other changes to *msg* as well, such as adding
      various MIME headers to encode information needed to interpret the stored
      data.

      To find the handler, obtain the type of *obj* (``typ = type(obj)``), and
      look for the following keys in the registry, stopping with the first one
      found:

           * the type itself (``typ``)
           * the type's fully qualified name (``typ.__module__ + '.' +
             typ.__qualname__``).
           * the type's qualname (``typ.__qualname__``)
           * the type's name (``typ.__name__``).

      If none of the above match, repeat all of the checks above for each of
      the types in the :term:`MRO` (``typ.__mro__``).  Finally, if no other key
      yields a handler, check for a handler for the key ``None``.  If there is
      no handler for ``None``, raise a :exc:`KeyError` for the fully
      qualified name of the type.

      Also add a :mailheader:`MIME-Version` header if one is not present (see
      also :class:`.MIMEPart`).


   .. method:: add_get_handler(key, handler)

      Record the function *handler* as the handler for *key*.  For the possible
      values of *key*, see :meth:`get_content`.


   .. method:: add_set_handler(typekey, handler)

      Record *handler* as the function to call when an object of a type
      matching *typekey* is passed to :meth:`set_content`.  For the possible
      values of *typekey*, see :meth:`set_content`.


Content Manager Instances
~~~~~~~~~~~~~~~~~~~~~~~~~

Currently the email package provides only one concrete content manager,
:data:`raw_data_manager`, although more may be added in the future.
:data:`raw_data_manager` is the
:attr:`~email.policy.EmailPolicy.content_manager` provided by
:attr:`~email.policy.EmailPolicy` and its derivatives.


.. data:: raw_data_manager

   This content manager provides only a minimum interface beyond that provided
   by :class:`~email.message.Message` itself:  it deals only with text, raw
   byte strings, and :class:`~email.message.Message` objects.  Nevertheless, it
   provides significant advantages compared to the base API: ``get_content`` on
   a text part will return a unicode string without the application needing to
   manually decode it, ``set_content`` provides a rich set of options for
   controlling the headers added to a part and controlling the content transfer
   encoding, and it enables the use of the various ``add_`` methods, thereby
   simplifying the creation of multipart messages.

   .. method:: get_content(msg, errors='replace')

      Return the payload of the part as either a string (for ``text`` parts), an
      :class:`~email.message.EmailMessage` object (for ``message/rfc822``
      parts), or a ``bytes`` object (for all other non-multipart types).  Raise
      a :exc:`KeyError` if called on a ``multipart``.  If the part is a
      ``text`` part and *errors* is specified, use it as the error handler when
      decoding the payload to unicode.  The default error handler is
      ``replace``.

   .. method:: set_content(msg, <'str'>, subtype="plain", charset='utf-8', \
                           cte=None, \
                           disposition=None, filename=None, cid=None, \
                           params=None, headers=None)
               set_content(msg, <'bytes'>, maintype, subtype, cte="base64", \
                           disposition=None, filename=None, cid=None, \
                           params=None, headers=None)
               set_content(msg, <'EmailMessage'>, cte=None, \
                           disposition=None, filename=None, cid=None, \
                           params=None, headers=None)

       Add headers and payload to *msg*:

       Add a :mailheader:`Content-Type` header with a ``maintype/subtype``
       value.

           * For ``str``, set the MIME ``maintype`` to ``text``, and set the
             subtype to *subtype* if it is specified, or ``plain`` if it is not.
           * For ``bytes``, use the specified *maintype* and *subtype*, or
             raise a :exc:`TypeError` if they are not specified.
           * For :class:`~email.message.EmailMessage` objects, set the maintype
             to ``message``, and set the subtype to *subtype* if it is
             specified or ``rfc822`` if it is not.  If *subtype* is
             ``partial``, raise an error (``bytes`` objects must be used to
             construct ``message/partial`` parts).

       If *charset* is provided (which is valid only for ``str``), encode the
       string to bytes using the specified character set.  The default is
       ``utf-8``.  If the specified *charset* is a known alias for a standard
       MIME charset name, use the standard charset instead.

       If *cte* is set, encode the payload using the specified content transfer
       encoding, and set the :mailheader:`Content-Transfer-Encoding` header to
       that value.  Possible values for *cte* are ``quoted-printable``,
       ``base64``, ``7bit``, ``8bit``, and ``binary``.  If the input cannot be
       encoded in the specified encoding (for example, specifying a *cte* of
       ``7bit`` for an input that contains non-ASCII values), raise a
       :exc:`ValueError`.

            * For ``str`` objects, if *cte* is not set use heuristics to
              determine the most compact encoding.
            * For :class:`~email.message.EmailMessage`, per :rfc:`2046`, raise
              an error if a *cte* of ``quoted-printable`` or ``base64`` is
              requested for *subtype* ``rfc822``, and for any *cte* other than
              ``7bit`` for *subtype* ``external-body``.  For
              ``message/rfc822``, use ``8bit`` if *cte* is not specified.  For
              all other values of *subtype*, use ``7bit``.

       .. note:: A *cte* of ``binary`` does not actually work correctly yet.
          The ``EmailMessage`` object as modified by ``set_content`` is
          correct, but :class:`~email.generator.BytesGenerator` does not
          serialize it correctly.

       If *disposition* is set, use it as the value of the
       :mailheader:`Content-Disposition` header.  If not specified, and
       *filename* is specified, add the header with the value ``attachment``.
       If *disposition* is not specified and *filename* is also not specified,
       do not add the header.  The only valid values for *disposition* are
       ``attachment`` and ``inline``.

       If *filename* is specified, use it as the value of the ``filename``
       parameter of the :mailheader:`Content-Disposition` header.

       If *cid* is specified, add a :mailheader:`Content-ID` header with
       *cid* as its value.

       If *params* is specified, iterate its ``items`` method and use the
       resulting ``(key, value)`` pairs to set additional parameters on the
       :mailheader:`Content-Type` header.

       If *headers* is specified and is a list of strings of the form
       ``headername: headervalue`` or a list of ``header`` objects
       (distinguished from strings by having a ``name`` attribute), add the
       headers to *msg*.


.. rubric:: Footnotes

.. [1] Originally added in 3.4 as a :term:`provisional module <provisional
       package>`