diff --git a/docs/conf.py b/docs/conf.py index 659115dfbd8..39a280e464c 100644 --- a/docs/conf.py +++ b/docs/conf.py @@ -94,6 +94,7 @@ pygments_style = 'trac' intersphinx_mapping = { 'python': ('http://docs.python.org/2.7', None), 'sphinx': ('http://sphinx.pocoo.org/', None), + 'six': ('http://packages.python.org/six/', None), } # Python's docs don't change every week. diff --git a/docs/topics/python3.txt b/docs/topics/python3.txt index e4bfc1bd9cc..cfa38d9bec6 100644 --- a/docs/topics/python3.txt +++ b/docs/topics/python3.txt @@ -2,42 +2,34 @@ Python 3 compatibility ====================== -Django 1.5 is the first version of Django to support Python 3. - -The same code runs both on Python 2 (≥2.6.5) and Python 3 (≥3.2). To -achieve this: - -- wherever possible, Django uses the six_ compatibility layer, -- all modules declare ``from __future__ import unicode_literals``. +Django 1.5 is the first version of Django to support Python 3. The same code +runs both on Python 2 (≥ 2.6.5) and Python 3 (≥ 3.2), thanks to the six_ +compatibility layer and ``unicode_literals``. .. _six: http://packages.python.org/six/ This document is not meant as a Python 2 to Python 3 migration guide. There -are many existing resources, including `Python's official porting guide`_. But -it describes guidelines that apply to Django's code and are recommended for -pluggable apps that run with both Python 2 and 3. +are many existing resources, including `Python's official porting guide`_. +Rather, it describes guidelines that apply to Django's code and are +recommended for pluggable apps that run with both Python 2 and 3. .. _Python's official porting guide: http://docs.python.org/py3k/howto/pyporting.html -.. module: django.utils.six +Syntax requirements +=================== -django.utils.six -================ +Unicode +------- -Read the documentation of six_. It's the canonical compatibility library for -supporting Python 2 and 3 in a single codebase. +In Python 3, all strings are considered Unicode by default. The ``unicode`` +type from Python 2 is called ``str`` in Python 3, and ``str`` becomes +``bytes``. -``six`` is bundled with Django: you can import it as :mod:`django.utils.six`. +You mustn't use the ``u`` prefix before a unicode string literal because it's +a syntax error in Python 3.2. You must prefix byte strings with ``b``. -.. _string-handling: - -String handling -=============== - -In Python 3, all strings are considered Unicode strings by default. Byte -strings must be prefixed with the letter ``b``. In order to enable the same -behavior in Python 2, every module must import ``unicode_literals`` from -``__future__``:: +In order to enable the same behavior in Python 2, every module must import +``unicode_literals`` from ``__future__``:: from __future__ import unicode_literals @@ -47,3 +39,84 @@ behavior in Python 2, every module must import ``unicode_literals`` from Be cautious if you have to `slice bytestrings`_. .. _slice bytestrings: http://docs.python.org/py3k/howto/pyporting.html#bytes-literals + +Exceptions +---------- + +When you capture exceptions, use the ``as`` keyword:: + + try: + ... + except MyException as exc: + ... + +This older syntax was removed in Python 3:: + + try: + ... + except MyException, exc: + ... + +The syntax to reraise an exception with a different traceback also changed. +Use :func:`six.reraise`. + + +.. module: django.utils.six + +Writing compatible code with six +================================ + +six is the canonical compatibility library for supporting Python 2 and 3 in +a single codebase. Read its `documentation `_! + +:mod:`six` is bundled with Django: you can import it as :mod:`django.utils.six`. + +Here are the most common changes required to write compatible code. + +String types +------------ + +The ``basestring`` and ``unicode`` types were removed in Python 3, and the +meaning of ``str`` changed. To test these types, use the following idioms:: + + isinstance(myvalue, six.string_types) # replacement for basestring + isinstance(myvalue, six.text_type) # replacement for unicode + isinstance(myvalue, bytes) # replacement for str + +Python ≥ 2.6 provides ``bytes`` as an alias for ``str``, so you don't need +:attr:`six.binary_type`. + +``long`` +-------- + +The ``long`` type no longer exists in Python 3. ``1L`` is a syntax error. Use +:data:`six.integer_types` check if a value is an integer or a long:: + + isinstance(myvalue, six.integer_types) # replacement for (int, long) + +``xrange`` +---------- + +Import :func:`six.moves.xrange` wherever you use ``xrange``. + +Moved modules +------------- + +Some modules were renamed in Python 3. The :mod:`django.utils.six.moves +` module provides a compatible location to import them. + +In addition to six' defaults, Django's version provides ``dummy_thread`` as +``_dummy_thread``. + +PY3 +--- + +If you need different code in Python 2 and Python 3, check :data:`six.PY3`:: + + if six.PY3: + # do stuff Python 3-wise + else: + # do stuff Python 2-wise + +This is a last resort solution when :mod:`six` doesn't provide an appropriate +function.