Commit 5e6ded2e authored by Claude Paroz's avatar Claude Paroz
Browse files

Fixed #18363 -- Added Python 3 compatibility layer. 

Thanks Vinay Sajip for the support of his django3 branch
and Alex Gaynor, kezabelle, YorikSar for the review.
parent 87ff89d1

django/utils/py3.py

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# Compatibility layer for running Django both in 2.x and 3.x



import sys



if sys.version_info[0] < 3:

    PY3 = False

    # Changed module locations

    from urlparse import (urlparse, urlunparse, urljoin, urlsplit, urlunsplit,

                          urldefrag, parse_qsl)

    from urllib import (quote, unquote, quote_plus, urlopen, urlencode,

                        url2pathname, urlretrieve, unquote_plus)

    from urllib2 import (Request, OpenerDirector, UnknownHandler, HTTPHandler,

                         HTTPSHandler, HTTPDefaultErrorHandler, FTPHandler,

                         HTTPError, HTTPErrorProcessor)

    import urllib2

    import Cookie as cookies

    try:

        import cPickle as pickle

    except ImportError:

        import pickle

    try:

        import thread

    except ImportError:

        import dummy_thread as thread

    from htmlentitydefs import name2codepoint

    import HTMLParser

    from os import getcwdu

    from itertools import izip as zip

    unichr = unichr

    xrange = xrange

    maxsize = sys.maxint



    # Type aliases

    string_types = basestring,

    text_type = unicode

    integer_types = int, long

    long_type = long



    from io import BytesIO as OutputIO



    # Glue code for syntax differences

    def reraise(tp, value, tb=None):

        exec("raise tp, value, tb")



    def with_metaclass(meta, base=object):

        class _DjangoBase(base):

            __metaclass__ = meta

        return _DjangoBase



    iteritems = lambda o: o.iteritems()

    itervalues = lambda o: o.itervalues()

    iterkeys = lambda o: o.iterkeys()



    # n() is useful when python3 needs a str (unicode), and python2 str (bytes)

    n = lambda s: s.encode('utf-8')



else:

    PY3 = True

    import builtins



    # Changed module locations

    from urllib.parse import (urlparse, urlunparse, urlencode, urljoin,

                              urlsplit, urlunsplit, quote, unquote,

                              quote_plus, unquote_plus, parse_qsl,

                              urldefrag)

    from urllib.request import (urlopen, url2pathname, Request, OpenerDirector,

                                UnknownHandler, HTTPHandler, HTTPSHandler,

                                HTTPDefaultErrorHandler, FTPHandler,

                                HTTPError, HTTPErrorProcessor, urlretrieve)

    import urllib.request as urllib2

    import http.cookies as cookies

    import pickle

    try:

        import _thread as thread

    except ImportError:

        import _dummy_thread as thread

    from html.entities import name2codepoint

    import html.parser as HTMLParser

    from os import getcwd as getcwdu

    zip = zip

    unichr = chr

    xrange = range

    maxsize = sys.maxsize



    # Type aliases

    string_types = str,

    text_type = str

    integer_types = int,

    long_type = int



    from io import StringIO as OutputIO



    # Glue code for syntax differences

    def reraise(tp, value, tb=None):

        if value.__traceback__ is not tb:

            raise value.with_traceback(tb)

        raise value



    def with_metaclass(meta, base=object):

        ns = dict(base=base, meta=meta)

        exec("""class _DjangoBase(base, metaclass=meta):

    pass""", ns)

        return ns["_DjangoBase"]



    iteritems = lambda o: o.items()

    itervalues = lambda o: o.values()

    iterkeys = lambda o: o.keys()



    n = lambda s: s

docs/index.txt

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@@ -183,6 +183,7 @@ Other batteries included 
* :doc:`Logging <topics/logging>`

* :doc:`Messages <ref/contrib/messages>`

* :doc:`Pagination <topics/pagination>`

* :doc:`Python 3 compatibility <topics/python3>`

* :doc:`Redirects <ref/contrib/redirects>`

* :doc:`Security <topics/security>`

* :doc:`Serialization <topics/serialization>`

docs/ref/unicode.txt

+2 −1
Original line number Diff line number Diff line
@@ -66,6 +66,7 @@ Python 2 with unicode literals or Python 3:: 
    my_string = b"This is a bytestring"

    my_unicode = "This is an Unicode string"



See also :doc:`Python 3 compatibility </topics/python3>`.



.. admonition:: Warning

docs/topics/index.txt

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Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ Introductions to all the key parts of Django you'll need to know: 
   i18n/index

   logging

   pagination

   python3

   security

   serialization

   settings

docs/topics/python3.txt

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======================

Python 3 compatibility

======================



Django 1.5 introduces a compatibility layer that allows the code to be run both

in Python 2 (2.6/2.7) and Python 3 (>= 3.2) (*work in progress*).



This document is not meant as a complete Python 2 to Python 3 migration guide.

There are many existing resources you can read. But we describe some utilities

and guidelines that we recommend you should use when you want to ensure your

code can be run with both Python 2 and 3.



* http://docs.python.org/py3k/howto/pyporting.html

* http://python3porting.com/



django.utils.py3

================



Whenever a symbol or module has different semantics or different locations on

Python 2 and Python 3, you can import it from ``django.utils.py3`` where it

will be automatically converted depending on your current Python version.



PY3

---



If you need to know anywhere in your code if you are running Python 3 or a

previous Python 2 version, you can check the ``PY3`` boolean variable::



    from django.utils.py3 import PY3



    if PY3:

        # Do stuff Python 3-wise

    else:

        # Do stuff Python 2-wise



This should be considered as a last resort solution when it is not possible

to import a compatible name from django.utils.py3, as described in the sections

below.



String handling

===============



In Python 3, all strings are considered Unicode strings by default. Byte strings

have to be prefixed with the letter 'b'. To mimic the same behaviour in Python 2,

we recommend you import ``unicode_literals`` from the ``__future__`` library::



    from __future__ import unicode_literals



    my_string = "This is an unicode literal"

    my_bytestring = b"This is a bytestring"



Be cautious if you have to slice bytestrings.

See http://docs.python.org/py3k/howto/pyporting.html#bytes-literals



Different expected strings

--------------------------



Some method parameters have changed the expected string type of a parameter.

For example, ``strftime`` format parameter expects a bytestring on Python 2 but

a normal (Unicode) string on Python 3. For these cases, ``django.utils.py3``

provides a ``n()`` function which encodes the string parameter only with

Python 2.



    >>> from __future__ import unicode_literals

    >>> from datetime import datetime



    >>> print(datetime.date(2012, 5, 21).strftime(n("%m → %Y")))

    05 → 2012



Renamed types

=============



Several types are named differently in Python 2 and Python 3. In order to keep

compatibility while using those types, import their corresponding aliases from

``django.utils.py3``.



===========  =========  =====================

Python 2     Python 3   django.utils.py3

===========  =========  =====================

basestring,  str,       string_types (tuple)

unicode      str        text_type

int, long    int,       integer_types (tuple)

long         int        long_type

===========  =========  =====================



String aliases

--------------



Code sample::



    if isinstance(foo, basestring):

        print("foo is a string")



    # I want to convert a number to a Unicode string

    bar = 45

    bar_string = unicode(bar)



Should be replaced by::



    from django.utils.py3 import string_types, text_type



    if isinstance(foo, string_types):

        print("foo is a string")



    # I want to convert a number to a Unicode string

    bar = 45

    bar_string = text_type(bar)



No more long type

-----------------



``long`` and ``int`` types have been unified in Python 3, meaning that  ``long``

is no longer available. ``django.utils.py3`` provides both ``long_type`` and

``integer_types`` aliases. For example:



.. code-block:: python



    # Old Python 2 code

    my_var = long(333463247234623)

    if isinstance(my_var, (int, long)):

        # ...



Should be replaced by:



.. code-block:: python



    from django.utils.py3 import long_type, integer_types



    my_var = long_type(333463247234623)

    if isinstance(my_var, integer_types):

        # ...





Changed module locations

========================



The following modules have changed their location in Python 3. Therefore, it is

recommended to import them from the ``django.utils.py3`` compatibility layer:



=============================== ======================================  ======================

Python 2                        Python3                                 django.utils.py3

=============================== ======================================  ======================

Cookie                          http.cookies                            cookies



urlparse.urlparse               urllib.parse.urlparse                   urlparse

urlparse.urlunparse             urllib.parse.urlunparse                 urlunparse

urlparse.urljoin                urllib.parse.urljoin                    urljoin

urlparse.urlsplit               urllib.parse.urlsplit                   urlsplit

urlparse.urlunsplit             urllib.parse.urlunsplit                 urlunsplit

urlparse.urldefrag              urllib.parse.urldefrag                  urldefrag

urlparse.parse_qsl              urllib.parse.parse_qsl                  parse_qsl

urllib.quote                    urllib.parse.quote                      quote

urllib.unquote                  urllib.parse.unquote                    unquote

urllib.quote_plus               urllib.parse.quote_plus                 quote_plus

urllib.unquote_plus             urllib.parse.unquote_plus               unquote_plus

urllib.urlencode                urllib.parse.urlencode                  urlencode

urllib.urlopen                  urllib.request.urlopen                  urlopen

urllib.url2pathname             urllib.request.url2pathname             url2pathname

urllib.urlretrieve              urllib.request.urlretrieve              urlretrieve

urllib2                         urllib.request                          urllib2

urllib2.Request                 urllib.request.Request                  Request

urllib2.OpenerDirector          urllib.request.OpenerDirector           OpenerDirector

urllib2.UnknownHandler          urllib.request.UnknownHandler           UnknownHandler

urllib2.HTTPHandler             urllib.request.HTTPHandler              HTTPHandler

urllib2.HTTPSHandler            urllib.request.HTTPSHandler             HTTPSHandler

urllib2.HTTPDefaultErrorHandler urllib.request.HTTPDefaultErrorHandler  HTTPDefaultErrorHandler

urllib2.FTPHandler              urllib.request.FTPHandler               FTPHandler

urllib2.HTTPError               urllib.request.HTTPError                HTTPError

urllib2.HTTPErrorProcessor      urllib.request.HTTPErrorProcessor       HTTPErrorProcessor



htmlentitydefs.name2codepoint   html.entities.name2codepoint            name2codepoint

HTMLParser                      html.parser                             HTMLParser

cPickle/pickle                  pickle                                  pickle

thread/dummy_thread             _thread/_dummy_thread                   thread



os.getcwdu                      os.getcwd                               getcwdu

itertools.izip                  zip                                     zip

sys.maxint                      sys.maxsize                             maxsize

unichr                          chr                                     unichr

xrange                          range                                   xrange

=============================== ======================================  ======================





Ouptut encoding now Unicode

===========================



If you want to catch stdout/stderr output, the output content is UTF-8 encoded

in Python 2, while it is Unicode strings in Python 3. You can use the OutputIO

stream to capture this output::



    from django.utils.py3 import OutputIO



    try:

        old_stdout = sys.stdout

        out = OutputIO()

        sys.stdout = out

        # Do stuff which produces standard output

        result = out.getvalue()

    finally:

        sys.stdout = old_stdout



Dict iteritems/itervalues/iterkeys

==================================



The iteritems(), itervalues() and iterkeys() methods of dictionaries do not

exist any more in Python 3, simply because they represent the default items()

values() and keys() behavior in Python 3. Therefore, to keep compatibility,

use similar functions from ``django.utils.py3``::



    from django.utils.py3 import iteritems, itervalues, iterkeys



    my_dict = {'a': 21, 'b': 42}

    for key, value in iteritems(my_dict):

        # ...

    for value in itervalues(my_dict):

        # ...

    for key in iterkeys(my_dict):

        # ...



Note that in Python 3, dict.keys(), dict.items() and dict.values() return

"views" instead of lists. Wrap them into list() if you really need their return

values to be in a list.



http://docs.python.org/release/3.0.1/whatsnew/3.0.html#views-and-iterators-instead-of-lists



Metaclass

=========



The syntax for declaring metaclasses has changed in Python 3.

``django.utils.py3`` offers a compatible way to declare metaclasses::



    from django.utils.py3 import with_metaclass



    class MyClass(with_metaclass(SubClass1, SubClass2,...)):

        # ...



Re-raising exceptions

=====================



One of the syntaxes to raise exceptions (raise E, V, T) is gone in Python 3.

This is especially used in very specific cases where you want to re-raise a

different exception that the initial one, while keeping the original traceback.

So, instead of::



    raise Exception, Exception(msg), traceback



Use::



    from django.utils.py3 import reraise



    reraise(Exception, Exception(msg), traceback)