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+:mod:`email`: Representing an email message
+-------------------------------------------
+
+.. module:: email.message
+   :synopsis: The base class representing email messages.
+
+
+The central class in the :mod:`email` package is the :class:`Message` class,
+imported from the :mod:`email.message` module.  It is the base class for the
+:mod:`email` object model.  :class:`Message` provides the core functionality for
+setting and querying header fields, and for accessing message bodies.
+
+Conceptually, a :class:`Message` object consists of *headers* and *payloads*.
+Headers are :rfc:`2822` style field names and values where the field name and
+value are separated by a colon.  The colon is not part of either the field name
+or the field value.
+
+Headers are stored and returned in case-preserving form but are matched
+case-insensitively.  There may also be a single envelope header, also known as
+the *Unix-From* header or the ``From_`` header.  The payload is either a string
+in the case of simple message objects or a list of :class:`Message` objects for
+MIME container documents (e.g. :mimetype:`multipart/\*` and
+:mimetype:`message/rfc822`).
+
+:class:`Message` objects provide a mapping style interface for accessing the
+message headers, and an explicit interface for accessing both the headers and
+the payload.  It provides convenience methods for generating a flat text
+representation of the message object tree, for accessing commonly used header
+parameters, and for recursively walking over the object tree.
+
+Here are the methods of the :class:`Message` class:
+
+
+.. class:: Message()
+
+   The constructor takes no arguments.
+
+
+.. method:: Message.as_string([unixfrom])
+
+   Return the entire message flatten as a string.  When optional *unixfrom* is
+   ``True``, the envelope header is included in the returned string.  *unixfrom*
+   defaults to ``False``.
+
+   Note that this method is provided as a convenience and may not always format the
+   message the way you want.  For example, by default it mangles lines that begin
+   with ``From``.  For more flexibility, instantiate a :class:`Generator` instance
+   and use its :meth:`flatten` method directly.  For example::
+
+      from cStringIO import StringIO
+      from email.generator import Generator
+      fp = StringIO()
+      g = Generator(fp, mangle_from_=False, maxheaderlen=60)
+      g.flatten(msg)
+      text = fp.getvalue()
+
+
+.. method:: Message.__str__()
+
+   Equivalent to ``as_string(unixfrom=True)``.
+
+
+.. method:: Message.is_multipart()
+
+   Return ``True`` if the message's payload is a list of sub-\ :class:`Message`
+   objects, otherwise return ``False``.  When :meth:`is_multipart` returns False,
+   the payload should be a string object.
+
+
+.. method:: Message.set_unixfrom(unixfrom)
+
+   Set the message's envelope header to *unixfrom*, which should be a string.
+
+
+.. method:: Message.get_unixfrom()
+
+   Return the message's envelope header.  Defaults to ``None`` if the envelope
+   header was never set.
+
+
+.. method:: Message.attach(payload)
+
+   Add the given *payload* to the current payload, which must be ``None`` or a list
+   of :class:`Message` objects before the call. After the call, the payload will
+   always be a list of :class:`Message` objects.  If you want to set the payload to
+   a scalar object (e.g. a string), use :meth:`set_payload` instead.
+
+
+.. method:: Message.get_payload([i[, decode]])
+
+   Return a reference the current payload, which will be a list of :class:`Message`
+   objects when :meth:`is_multipart` is ``True``, or a string when
+   :meth:`is_multipart` is ``False``.  If the payload is a list and you mutate the
+   list object, you modify the message's payload in place.
+
+   With optional argument *i*, :meth:`get_payload` will return the *i*-th element
+   of the payload, counting from zero, if :meth:`is_multipart` is ``True``.  An
+   :exc:`IndexError` will be raised if *i* is less than 0 or greater than or equal
+   to the number of items in the payload.  If the payload is a string (i.e.
+   :meth:`is_multipart` is ``False``) and *i* is given, a :exc:`TypeError` is
+   raised.
+
+   Optional *decode* is a flag indicating whether the payload should be decoded or
+   not, according to the :mailheader:`Content-Transfer-Encoding` header. When
+   ``True`` and the message is not a multipart, the payload will be decoded if this
+   header's value is ``quoted-printable`` or ``base64``.  If some other encoding is
+   used, or :mailheader:`Content-Transfer-Encoding` header is missing, or if the
+   payload has bogus base64 data, the payload is returned as-is (undecoded).  If
+   the message is a multipart and the *decode* flag is ``True``, then ``None`` is
+   returned.  The default for *decode* is ``False``.
+
+
+.. method:: Message.set_payload(payload[, charset])
+
+   Set the entire message object's payload to *payload*.  It is the client's
+   responsibility to ensure the payload invariants.  Optional *charset* sets the
+   message's default character set; see :meth:`set_charset` for details.
+
+   .. versionchanged:: 2.2.2
+      *charset* argument added.
+
+
+.. method:: Message.set_charset(charset)
+
+   Set the character set of the payload to *charset*, which can either be a
+   :class:`Charset` instance (see :mod:`email.charset`), a string naming a
+   character set, or ``None``.  If it is a string, it will be converted to a
+   :class:`Charset` instance.  If *charset* is ``None``, the ``charset`` parameter
+   will be removed from the :mailheader:`Content-Type` header. Anything else will
+   generate a :exc:`TypeError`.
+
+   The message will be assumed to be of type :mimetype:`text/\*` encoded with
+   *charset.input_charset*.  It will be converted to *charset.output_charset* and
+   encoded properly, if needed, when generating the plain text representation of
+   the message.  MIME headers (:mailheader:`MIME-Version`,
+   :mailheader:`Content-Type`, :mailheader:`Content-Transfer-Encoding`) will be
+   added as needed.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.get_charset()
+
+   Return the :class:`Charset` instance associated with the message's payload.
+
+   .. versionadded:: 2.2.2
+
+The following methods implement a mapping-like interface for accessing the
+message's :rfc:`2822` headers.  Note that there are some semantic differences
+between these methods and a normal mapping (i.e. dictionary) interface.  For
+example, in a dictionary there are no duplicate keys, but here there may be
+duplicate message headers.  Also, in dictionaries there is no guaranteed order
+to the keys returned by :meth:`keys`, but in a :class:`Message` object, headers
+are always returned in the order they appeared in the original message, or were
+added to the message later.  Any header deleted and then re-added are always
+appended to the end of the header list.
+
+These semantic differences are intentional and are biased toward maximal
+convenience.
+
+Note that in all cases, any envelope header present in the message is not
+included in the mapping interface.
+
+
+.. method:: Message.__len__()
+
+   Return the total number of headers, including duplicates.
+
+
+.. method:: Message.__contains__(name)
+
+   Return true if the message object has a field named *name*. Matching is done
+   case-insensitively and *name* should not include the trailing colon.  Used for
+   the ``in`` operator, e.g.::
+
+      if 'message-id' in myMessage:
+          print 'Message-ID:', myMessage['message-id']
+
+
+.. method:: Message.__getitem__(name)
+
+   Return the value of the named header field.  *name* should not include the colon
+   field separator.  If the header is missing, ``None`` is returned; a
+   :exc:`KeyError` is never raised.
+
+   Note that if the named field appears more than once in the message's headers,
+   exactly which of those field values will be returned is undefined.  Use the
+   :meth:`get_all` method to get the values of all the extant named headers.
+
+
+.. method:: Message.__setitem__(name, val)
+
+   Add a header to the message with field name *name* and value *val*.  The field
+   is appended to the end of the message's existing fields.
+
+   Note that this does *not* overwrite or delete any existing header with the same
+   name.  If you want to ensure that the new header is the only one present in the
+   message with field name *name*, delete the field first, e.g.::
+
+      del msg['subject']
+      msg['subject'] = 'Python roolz!'
+
+
+.. method:: Message.__delitem__(name)
+
+   Delete all occurrences of the field with name *name* from the message's headers.
+   No exception is raised if the named field isn't present in the headers.
+
+
+.. method:: Message.has_key(name)
+
+   Return true if the message contains a header field named *name*, otherwise
+   return false.
+
+
+.. method:: Message.keys()
+
+   Return a list of all the message's header field names.
+
+
+.. method:: Message.values()
+
+   Return a list of all the message's field values.
+
+
+.. method:: Message.items()
+
+   Return a list of 2-tuples containing all the message's field headers and values.
+
+
+.. method:: Message.get(name[, failobj])
+
+   Return the value of the named header field.  This is identical to
+   :meth:`__getitem__` except that optional *failobj* is returned if the named
+   header is missing (defaults to ``None``).
+
+Here are some additional useful methods:
+
+
+.. method:: Message.get_all(name[, failobj])
+
+   Return a list of all the values for the field named *name*. If there are no such
+   named headers in the message, *failobj* is returned (defaults to ``None``).
+
+
+.. method:: Message.add_header(_name, _value, **_params)
+
+   Extended header setting.  This method is similar to :meth:`__setitem__` except
+   that additional header parameters can be provided as keyword arguments.  *_name*
+   is the header field to add and *_value* is the *primary* value for the header.
+
+   For each item in the keyword argument dictionary *_params*, the key is taken as
+   the parameter name, with underscores converted to dashes (since dashes are
+   illegal in Python identifiers).  Normally, the parameter will be added as
+   ``key="value"`` unless the value is ``None``, in which case only the key will be
+   added.
+
+   Here's an example::
+
+      msg.add_header('Content-Disposition', 'attachment', filename='bud.gif')
+
+   This will add a header that looks like ::
+
+      Content-Disposition: attachment; filename="bud.gif"
+
+
+.. method:: Message.replace_header(_name, _value)
+
+   Replace a header.  Replace the first header found in the message that matches
+   *_name*, retaining header order and field name case.  If no matching header was
+   found, a :exc:`KeyError` is raised.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.get_content_type()
+
+   Return the message's content type.  The returned string is coerced to lower case
+   of the form :mimetype:`maintype/subtype`.  If there was no
+   :mailheader:`Content-Type` header in the message the default type as given by
+   :meth:`get_default_type` will be returned.  Since according to :rfc:`2045`,
+   messages always have a default type, :meth:`get_content_type` will always return
+   a value.
+
+   :rfc:`2045` defines a message's default type to be :mimetype:`text/plain` unless
+   it appears inside a :mimetype:`multipart/digest` container, in which case it
+   would be :mimetype:`message/rfc822`.  If the :mailheader:`Content-Type` header
+   has an invalid type specification, :rfc:`2045` mandates that the default type be
+   :mimetype:`text/plain`.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.get_content_maintype()
+
+   Return the message's main content type.  This is the :mimetype:`maintype` part
+   of the string returned by :meth:`get_content_type`.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.get_content_subtype()
+
+   Return the message's sub-content type.  This is the :mimetype:`subtype` part of
+   the string returned by :meth:`get_content_type`.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.get_default_type()
+
+   Return the default content type.  Most messages have a default content type of
+   :mimetype:`text/plain`, except for messages that are subparts of
+   :mimetype:`multipart/digest` containers.  Such subparts have a default content
+   type of :mimetype:`message/rfc822`.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.set_default_type(ctype)
+
+   Set the default content type.  *ctype* should either be :mimetype:`text/plain`
+   or :mimetype:`message/rfc822`, although this is not enforced.  The default
+   content type is not stored in the :mailheader:`Content-Type` header.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.get_params([failobj[, header[, unquote]]])
+
+   Return the message's :mailheader:`Content-Type` parameters, as a list.  The
+   elements of the returned list are 2-tuples of key/value pairs, as split on the
+   ``'='`` sign.  The left hand side of the ``'='`` is the key, while the right
+   hand side is the value.  If there is no ``'='`` sign in the parameter the value
+   is the empty string, otherwise the value is as described in :meth:`get_param`
+   and is unquoted if optional *unquote* is ``True`` (the default).
+
+   Optional *failobj* is the object to return if there is no
+   :mailheader:`Content-Type` header.  Optional *header* is the header to search
+   instead of :mailheader:`Content-Type`.
+
+   .. versionchanged:: 2.2.2
+      *unquote* argument added.
+
+
+.. method:: Message.get_param(param[, failobj[, header[, unquote]]])
+
+   Return the value of the :mailheader:`Content-Type` header's parameter *param* as
+   a string.  If the message has no :mailheader:`Content-Type` header or if there
+   is no such parameter, then *failobj* is returned (defaults to ``None``).
+
+   Optional *header* if given, specifies the message header to use instead of
+   :mailheader:`Content-Type`.
+
+   Parameter keys are always compared case insensitively.  The return value can
+   either be a string, or a 3-tuple if the parameter was :rfc:`2231` encoded.  When
+   it's a 3-tuple, the elements of the value are of the form ``(CHARSET, LANGUAGE,
+   VALUE)``.  Note that both ``CHARSET`` and ``LANGUAGE`` can be ``None``, in which
+   case you should consider ``VALUE`` to be encoded in the ``us-ascii`` charset.
+   You can usually ignore ``LANGUAGE``.
+
+   If your application doesn't care whether the parameter was encoded as in
+   :rfc:`2231`, you can collapse the parameter value by calling
+   :func:`email.Utils.collapse_rfc2231_value`, passing in the return value from
+   :meth:`get_param`.  This will return a suitably decoded Unicode string whn the
+   value is a tuple, or the original string unquoted if it isn't.  For example::
+
+      rawparam = msg.get_param('foo')
+      param = email.Utils.collapse_rfc2231_value(rawparam)
+
+   In any case, the parameter value (either the returned string, or the ``VALUE``
+   item in the 3-tuple) is always unquoted, unless *unquote* is set to ``False``.
+
+   .. versionchanged:: 2.2.2
+      *unquote* argument added, and 3-tuple return value possible.
+
+
+.. method:: Message.set_param(param, value[, header[, requote[, charset[, language]]]])
+
+   Set a parameter in the :mailheader:`Content-Type` header.  If the parameter
+   already exists in the header, its value will be replaced with *value*.  If the
+   :mailheader:`Content-Type` header as not yet been defined for this message, it
+   will be set to :mimetype:`text/plain` and the new parameter value will be
+   appended as per :rfc:`2045`.
+
+   Optional *header* specifies an alternative header to :mailheader:`Content-Type`,
+   and all parameters will be quoted as necessary unless optional *requote* is
+   ``False`` (the default is ``True``).
+
+   If optional *charset* is specified, the parameter will be encoded according to
+   :rfc:`2231`. Optional *language* specifies the RFC 2231 language, defaulting to
+   the empty string.  Both *charset* and *language* should be strings.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.del_param(param[, header[, requote]])
+
+   Remove the given parameter completely from the :mailheader:`Content-Type`
+   header.  The header will be re-written in place without the parameter or its
+   value.  All values will be quoted as necessary unless *requote* is ``False``
+   (the default is ``True``).  Optional *header* specifies an alternative to
+   :mailheader:`Content-Type`.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.set_type(type[, header][, requote])
+
+   Set the main type and subtype for the :mailheader:`Content-Type` header. *type*
+   must be a string in the form :mimetype:`maintype/subtype`, otherwise a
+   :exc:`ValueError` is raised.
+
+   This method replaces the :mailheader:`Content-Type` header, keeping all the
+   parameters in place.  If *requote* is ``False``, this leaves the existing
+   header's quoting as is, otherwise the parameters will be quoted (the default).
+
+   An alternative header can be specified in the *header* argument. When the
+   :mailheader:`Content-Type` header is set a :mailheader:`MIME-Version` header is
+   also added.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.get_filename([failobj])
+
+   Return the value of the ``filename`` parameter of the
+   :mailheader:`Content-Disposition` header of the message.  If the header does not
+   have a ``filename`` parameter, this method falls back to looking for the
+   ``name`` parameter.  If neither is found, or the header is missing, then
+   *failobj* is returned.  The returned string will always be unquoted as per
+   :meth:`Utils.unquote`.
+
+
+.. method:: Message.get_boundary([failobj])
+
+   Return the value of the ``boundary`` parameter of the :mailheader:`Content-Type`
+   header of the message, or *failobj* if either the header is missing, or has no
+   ``boundary`` parameter.  The returned string will always be unquoted as per
+   :meth:`Utils.unquote`.
+
+
+.. method:: Message.set_boundary(boundary)
+
+   Set the ``boundary`` parameter of the :mailheader:`Content-Type` header to
+   *boundary*.  :meth:`set_boundary` will always quote *boundary* if necessary.  A
+   :exc:`HeaderParseError` is raised if the message object has no
+   :mailheader:`Content-Type` header.
+
+   Note that using this method is subtly different than deleting the old
+   :mailheader:`Content-Type` header and adding a new one with the new boundary via
+   :meth:`add_header`, because :meth:`set_boundary` preserves the order of the
+   :mailheader:`Content-Type` header in the list of headers. However, it does *not*
+   preserve any continuation lines which may have been present in the original
+   :mailheader:`Content-Type` header.
+
+
+.. method:: Message.get_content_charset([failobj])
+
+   Return the ``charset`` parameter of the :mailheader:`Content-Type` header,
+   coerced to lower case.  If there is no :mailheader:`Content-Type` header, or if
+   that header has no ``charset`` parameter, *failobj* is returned.
+
+   Note that this method differs from :meth:`get_charset` which returns the
+   :class:`Charset` instance for the default encoding of the message body.
+
+   .. versionadded:: 2.2.2
+
+
+.. method:: Message.get_charsets([failobj])
+
+   Return a list containing the character set names in the message.  If the message
+   is a :mimetype:`multipart`, then the list will contain one element for each
+   subpart in the payload, otherwise, it will be a list of length 1.
+
+   Each item in the list will be a string which is the value of the ``charset``
+   parameter in the :mailheader:`Content-Type` header for the represented subpart.
+   However, if the subpart has no :mailheader:`Content-Type` header, no ``charset``
+   parameter, or is not of the :mimetype:`text` main MIME type, then that item in
+   the returned list will be *failobj*.
+
+
+.. method:: Message.walk()
+
+   The :meth:`walk` method is an all-purpose generator which can be used to iterate
+   over all the parts and subparts of a message object tree, in depth-first
+   traversal order.  You will typically use :meth:`walk` as the iterator in a
+   ``for`` loop; each iteration returns the next subpart.
+
+   Here's an example that prints the MIME type of every part of a multipart message
+   structure::
+
+      >>> for part in msg.walk():
+      ...     print part.get_content_type()
+      multipart/report
+      text/plain
+      message/delivery-status
+      text/plain
+      text/plain
+      message/rfc822
+
+.. versionchanged:: 2.5
+   The previously deprecated methods :meth:`get_type`, :meth:`get_main_type`, and
+   :meth:`get_subtype` were removed.
+
+:class:`Message` objects can also optionally contain two instance attributes,
+which can be used when generating the plain text of a MIME message.
+
+
+.. data:: preamble
+
+   The format of a MIME document allows for some text between the blank line
+   following the headers, and the first multipart boundary string. Normally, this
+   text is never visible in a MIME-aware mail reader because it falls outside the
+   standard MIME armor.  However, when viewing the raw text of the message, or when
+   viewing the message in a non-MIME aware reader, this text can become visible.
+
+   The *preamble* attribute contains this leading extra-armor text for MIME
+   documents.  When the :class:`Parser` discovers some text after the headers but
+   before the first boundary string, it assigns this text to the message's
+   *preamble* attribute.  When the :class:`Generator` is writing out the plain text
+   representation of a MIME message, and it finds the message has a *preamble*
+   attribute, it will write this text in the area between the headers and the first
+   boundary.  See :mod:`email.parser` and :mod:`email.generator` for details.
+
+   Note that if the message object has no preamble, the *preamble* attribute will
+   be ``None``.
+
+
+.. data:: epilogue
+
+   The *epilogue* attribute acts the same way as the *preamble* attribute, except
+   that it contains text that appears between the last boundary and the end of the
+   message.
+
+   .. versionchanged:: 2.5
+      You do not need to set the epilogue to the empty string in order for the
+      :class:`Generator` to print a newline at the end of the file.
+
+
+.. data:: defects
+
+   The *defects* attribute contains a list of all the problems found when parsing
+   this message.  See :mod:`email.errors` for a detailed description of the
+   possible parsing defects.
+
+   .. versionadded:: 2.4
+