Cleanups for when we drop Python 2 compatibility

[Tim Graham]

This is a tracking ticket of things that we can remove when we drop Python 2 compatibility in Django 2.0. Please edit the description of the ticket as you come across new items.

• django.core.mail.message.make_msgid() #23905
• django.dispatch.weakref_backports
• django.http.cookie workarounds (remains for Python 3.4)
• django.utils.2to3_fixes
• django.utils.decorators.ContextDecorator
• django.utils.encoding
  • @python_2_unicode_compatible
  • force/smart _unicode
  • either force/smart _text or force/smart _str
• django.utils.html_parser.use_workaround
• django.utils.http functions like urlquote_plus -- I think the versions of these functions on Python 3 don't have the unicode characters bug we are working around.
• Stop using django.utils.lru_cache
• Figure the deprecation plan for django.utils.lru_cache (staying for now)
• django.utils.six
• from __future__ import unicode_literals
• str() stuff for environment variables, e.g. 0bfb53866199f366ed140d49938fd185e5898156
• str() stuff for type(name) and __name__
• Inheriting from object in django.core.servers.basehttp (and perhaps other places) ala 4ee06ec3fc8e94d164afbd2f9c880c60c658a9ac
• git grep 'long int' (mostly docs)
• django.utils._os [npath,upath]
• In tests: contextlib.closing(self.urlopen (contextlib.closing no longer needed)
• Support for pysqlite (doesn't support Python 3)
• Replace super(ClassName, self) with super() ​PR
• Remove # -*- coding: utf-8 -*- source file encoding (that's the default on Python 3)
• Evaluate replacement of custom __del__ methods by ​weakref.finalize
• Remove __ne__ from objects already defining a __eq__
• Remove note about PYTHONHASHSEED (see #26243)
• Remove Field.creation_counter (replace by metaclass __prepare__ returning OrderedDict(), ​https://docs.python.org/3/reference/datamodel.html#preparing-the-class-namespace)
• django.test.utils.reset_warning_registry()
• Replace errno checks by IOError subclasses defined by ​PEP 3151
• django.utils.glob
• django.utils.cookies.SimpleCookie (remains for Python 3.4 compatibility)
• django.test.mock
• Replace tempfile.mkdtemp + remove with tempfile.TemporaryDirectory context manager ​PR
• Replace io.open() by a plain open()
• Evaluate need for assertRegex, assertRaisesRegex in tests. Some usage is merely to account for differences in messages between Python 2 and 3.
• re.U, re.UNICODE (default behavior of Python 3) - ​PR 7879

[Wojtek Ruszczewski]

Various nonlocal workarounds (​example).

[Anssi Kääriäinen]

I believe we can get rid of the Field.creation_counter hack. In Python 3 it is possible to store the attrs in a sorted dictionary. See ​http://stackoverflow.com/questions/4459531/how-to-read-class-attributes-in-the-same-order-as-declared.

[Curtis Maloney]

In far too many tests we rely on the fact six aliases builtins [like input] instead of using mock.

I submitted a patch recently to clean up a couple of these I found, but I am finding more.

[Claude Paroz]

Note that I have a local branch which does some boring removals (unicode_literals, utf-8 preambles, some six usage). So ping me as soon as the Django 2.0 deprecated stuff is removed and I'll offer a patch for that.

[Asif Saifuddin Auvi]

I am also working to remove python2 workarounds by following a module by module approach.

[Aymeric Augustin]

If Claude has already prepared these changes, perhaps you should wait for his patch instead of duplicating his work?

[Asif Saifuddin Auvi]

Replying to Aymeric Augustin:

If Claude has already prepared these changes, perhaps you should wait for his patch instead of duplicating his work?

Yes I talked with Claude on IRC to pause before his work is merged.

[Josh Smeaton]

Replying to Anssi Kääriäinen:

I believe we can get rid of the Field.creation_counter hack. In Python 3 it is possible to store the attrs in a sorted dictionary. See ​http://stackoverflow.com/questions/4459531/how-to-read-class-attributes-in-the-same-order-as-declared.

We could also remove this when we support python 3.6, as class attributes retain their order. I'm guessing this is a consequence (or the cause of) dictionaries retaining insertion order. ​https://docs.python.org/3.6/whatsnew/3.6.html#pep-520-preserving-class-attribute-definition-order

[Claude Paroz <claude@…>]

In d7b9aaa:

Refs #23919 -- Removed encoding preambles and future imports

[Claude Paroz <claude@…>]

In f3c43ad:

Refs #23919 -- Removed python_2_unicode_compatible decorator usage

[Tim Graham]

​PR for removing Python 2 references from docs.

[Claude Paroz <claude@…>]

In c716fe87:

Refs #23919 -- Removed six.PY2/PY3 usage

Thanks Tim Graham for the review.

[GitHub <noreply@…>]

In f6acd1d:

Refs #23919 -- Removed Python 2 notes in docs.

[Claude Paroz <claude@…>]

In 7b2f2e74:

Refs #23919 -- Removed six.<various>_types usage

Thanks Tim Graham and Simon Charette for the reviews.

[Claude Paroz <claude@…>]

In 2b281cc3:

Refs #23919 -- Removed most of remaining six usage

Thanks Tim Graham for the review.

[Tim Graham <timograham@…>]

In 3cc5f01d:

Refs #23919 -- Stopped using django.utils.lru_cache().

[Tim Graham <timograham@…>]

In eb422e47:

Refs #23919 -- Removed obsolete ne() methods.

ne() defaults to the opposite of eq() on Python 3
when it doesn't return NotImplemented.

[Tim Graham <timograham@…>]

In a5563963:

Refs #23919 -- Replaced io.open() with open().

io.open() is an alias for open() on Python 3.

[Claude Paroz <claude@…>]

In cecc079:

Refs #23919 -- Stopped inheriting from object to define new style classes.

[GitHub <noreply@…>]

In 5320fa7:

Refs #23919 -- Removed obsolete contextlib.closing() calls (for Python 2).

[GitHub <noreply@…>]

In e5c67f0:

Refs #23919 -- Removed reset_warning_registry() workaround for Python < 3.4.2.

[Simon Charette <charette.s@…>]

In 4c5ed3e6:

Refs #23919 -- Removed nonzero() methods (for Python 2).

Thanks Tim for the review.

[Tim Graham <timograham@…>]

In 41e0033c:

Refs #23919 -- Removed usage of django.utils.decorators.ContextDecorator.

[Simon Charette <charette.s@…>]

In 9695b14:

Refs #23919 -- Removed str() conversion of type and method name.

[GitHub <noreply@…>]

In d4bb3759:

Refs #23919 -- Removed obsolete compare_digest() and pbkdf2() implementations.

[GitHub <noreply@…>]

In 9e917cc2:

Fixed #23905, refs #23919 -- Used make_msgid() from stdlib.

[GitHub <noreply@…>]

In 9d27478:

Refs #23919 -- Removed docs references to long integers.

[Tim Graham <timograham@…>]

In 9ee47ce7:

Refs #23919 -- Removed enum ImportError handling for Python 2.

[Tim Graham <timograham@…>]

In eb0b921c:

Refs #23919 -- Removed SessionBase.iterkeys(), itervalues(), iteritems().

These methods only work on Python 2.

[Tim Graham <timograham@…>]

In fedda6d:

Refs #23919 -- Removed Python 2 version check in django.http.cookie.

[Tim Graham <timograham@…>]

In bf1c9570:

Refs #23919 -- Removed Python 2 workaround for hashing Oracle params (refs #27632).

[Claude Paroz <claude@…>]

In dc8834ca:

Refs #23919 -- Removed unneeded force_str calls

[Aymeric Augustin <aymeric.augustin@…>]

In 109b33f:

Refs #23919 -- Simplified assertRaisesRegex()'s that accounted for Python 2.

[GitHub <noreply@…>]

In 4e729fea:

Refs #23919 -- Removed django.utils._os.upath()/npath()/abspathu() usage.

These functions do nothing on Python 3.

[Claude Paroz <claude@…>]

In 042b735:

Refs #23919 -- Removed unneeded str() calls

[Tim Graham <timograham@…>]

In 7aba691:

Refs #23919 -- Removed django.test.mock Python 2 compatibility shim.

[Claude Paroz <claude@…>]

In 289fc1bf:

Refs #23919 -- Removed str_prefix usage

[Tim Graham <timograham@…>]

In 1b06d5e6:

Refs #23919 -- Removed pysqlite support (it's Python 2 only).

[GitHub <noreply@…>]

In 9e6e32bf:

Refs #23919 -- Removed django.utils.decorators.available_attrs() usage.

It's only needed to workaround a bug on Python 2.

[Tim Graham <timograham@…>]

In c222122:

Refs #23919 -- Removed re.U and re.UNICODE (default on Python 3).

[GitHub <noreply@…>]

In d170c63:

Refs #23919 -- Removed misc references to Python 2.

[Claude Paroz <claude@…>]

In 6e55e1d:

Refs #23919 -- Replaced six.reraise by raise