Version 1 of the email package was bundled with Python
releases up to Python 2.2.1. Version 2 was developed for the Python
2.3 release, and backported to Python 2.2.2. It was also available as
a separate distutils based package. email version 2 is
almost entirely backward compatible with version 1, with the
following differences:
The email.Header and email.Charset modules
have been added.
The pickle format for Message instances has changed.
Since this was never (and still isn't) formally defined, this
isn't considered a backward incompatibility. However if your
application pickles and unpickles Message instances, be
aware that in email version 2, Message
instances now have private variables _charset and
_default_type.
Several methods in the Message class have been
deprecated, or their signatures changed. Also, many new methods
have been added. See the documentation for the Message
class for details. The changes should be completely backward
compatible.
The object structure has changed in the face of
message/rfc822 content types. In email
version 1, such a type would be represented by a scalar payload,
i.e. the container message's is_multipart() returned
false, get_payload() was not a list object, but a single
Message instance.
This structure was inconsistent with the rest of the package, so
the object representation for message/rfc822 content
types was changed. In email version 2, the container
does return True from is_multipart(), and
get_payload() returns a list containing a single
Message item.
Note that this is one place that backward compatibility could
not be completely maintained. However, if you're already
testing the return type of get_payload(), you should be
fine. You just need to make sure your code doesn't do a
set_payload() with a Message instance on a
container with a content type of message/rfc822.
The Parser constructor's strict argument was
added, and its parse() and parsestr() methods
grew a headersonly argument. The strict flag was
also added to functions email.message_from_file()
and email.message_from_string().
Generator.__call__() is deprecated; use
Generator.flatten() instead. The Generator
class has also grown the clone() method.
The DecodedGenerator class in the
email.Generator module was added.
The intermediate base classes MIMENonMultipart and
MIMEMultipart have been added, and interposed in the
class hierarchy for most of the other MIME-related derived
classes.
The _encoder argument to the MIMEText constructor
has been deprecated. Encoding now happens implicitly based
on the _charset argument.
The following functions in the email.Utils module have
been deprecated: dump_address_pairs(),
decode(), and encode(). The following
functions have been added to the module:
make_msgid(), decode_rfc2231(),
encode_rfc2231(), and decode_params().
The non-public function email.Iterators._structure()
was added.
