changeset: 77151:331cceee3b45 user: R David Murray date: Fri May 25 22:25:56 2012 -0400 files: Doc/whatsnew/3.3.rst description: #12586: Expand What's New email entry with provisional policy features. diff -r cb62c958dd6a -r 331cceee3b45 Doc/whatsnew/3.3.rst --- a/Doc/whatsnew/3.3.rst Sat May 26 09:55:28 2012 +0800 +++ b/Doc/whatsnew/3.3.rst Fri May 25 22:25:56 2012 -0400 @@ -558,6 +558,9 @@ New Email Package Features ========================== +Policy Framework +---------------- + The email package now has a :mod:`~email.policy` framework. A :class:`~email.policy.Policy` is an object with several methods and properties that control how the email package behaves. The primary policy for Python 3.3 @@ -610,6 +613,99 @@ the ``generator``. +Provisional Policy with New Header API +-------------------------------------- + +While the policy framework is worthwhile all by itself, the main motivation for +introducing it is to allow the creation of new policies that implement new +features for the email package in a way that maintains backward compatibility +for those who do not use the new policies. Because the new policies introduce a +new API, we are releasing them in Python 3.3 as a :term:`provisional policy +`. Backwards incompatible changes (up to and including +removal of the code) may occur if deemed necessary by the core developers. + +The new policies are instances of :class:`~email.policy.EmailPolicy`, +and add the following additional controls: + + =============== ======================================================= + refold_source Controls whether or not headers parsed by a + :mod:`~email.parser` are refolded by the + :mod:`~email.generator`. It can be ``none``, ``long``, + or ``all``. The default is ``long``, which means that + source headers with a line longer than + ``max_line_length`` get refolded. ``none`` means no + line get refolded, and ``all`` means that all lines + get refolded. + + header_factory A callable that take a ``name`` and ``value`` and + produces a custom header object. + =============== ======================================================= + +The ``header_factory`` is the key to the new features provided by the new +policies. When one of the new policies is used, any header retrieved from +a ``Message`` object is an object produced by the ``header_factory``, and any +time you set a header on a ``Message`` it becomes an object produced by +``header_factory``. All such header objects have a ``name`` attribute equal +to the header name. Address and Date headers have additional attributes +that give you access to the parsed data of the header. This means you can now +do things like this:: + + >>> m = Message(policy=SMTP) + >>> m['To'] = 'Éric ' + >>> m['to'] + 'Éric ' + >>> m['to'].addresses + (Address(display_name='Éric', username='foo', domain='example.com'),) + >>> m['to'].addresses[0].username + 'foo' + >>> m['to'].addresses[0].display_name + 'Éric' + >>> m['Date'] = email.utils.localtime() + >>> m['Date'].datetime + datetime.datetime(2012, 5, 25, 21, 39, 24, 465484, tzinfo=datetime.timezone(datetime.timedelta(-1, 72000), 'EDT')) + >>> m['Date'] + 'Fri, 25 May 2012 21:44:27 -0400' + >>> print(m) + To: =?utf-8?q?=C3=89ric?= + Date: Fri, 25 May 2012 21:44:27 -0400 + +You will note that the unicode display name is automatically encoded as +``utf-8`` when the message is serialized, but that when the header is accessed +directly, you get the unicode version. This eliminates any need to deal with +the :mod:`email.header` :meth:`~email.header.decode_header` or +:meth:`~email.header.make_header` functions. + +You can also create addresses from parts:: + + >>> m['cc'] = [Group('pals', [Address('Bob', 'bob', 'example.com'), + ... Address('Sally', 'sally', 'example.com')]), + ... Address('Bonzo', addr_spec='bonz@laugh.com')] + >>> print(m) + To: =?utf-8?q?=C3=89ric?= + Date: Fri, 25 May 2012 21:44:27 -0400 + cc: pals: Bob , Sally ;, Bonzo + +Decoding to unicode is done automatically:: + + >>> m2 = message_from_string(str(m)) + >>> m2['to'] + 'Éric ' + +When you parse a message, you can use the ``addresses`` and ``groups`` +attributes of the header objects to access the groups and individual +addresses:: + + >>> m2['cc'].addresses + (Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com'), Address(display_name='Bonzo', username='bonz', domain='laugh.com')) + >>> m2['cc'].groups + (Group(display_name='pals', addresses=(Address(display_name='Bob', username='bob', domain='example.com'), Address(display_name='Sally', username='sally', domain='example.com')), Group(display_name=None, addresses=(Address(display_name='Bonzo', username='bonz', domain='laugh.com'),)) + +In summary, if you use one of the new policies, header manipulation works the +way it ought to: your application works with unicode strings, and the email +package transparently encodes and decodes the unicode to and from the RFC +standard Content Transfer Encodings. + + Other Language Changes ======================