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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.
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# Compatibility layer for running Django both in 2.x and 3.x | ||
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import sys | ||
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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 | ||
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# Type aliases | ||
string_types = basestring, | ||
text_type = unicode | ||
integer_types = int, long | ||
long_type = long | ||
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from io import BytesIO as OutputIO | ||
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# Glue code for syntax differences | ||
def reraise(tp, value, tb=None): | ||
exec("raise tp, value, tb") | ||
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def with_metaclass(meta, base=object): | ||
class _DjangoBase(base): | ||
__metaclass__ = meta | ||
return _DjangoBase | ||
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iteritems = lambda o: o.iteritems() | ||
itervalues = lambda o: o.itervalues() | ||
iterkeys = lambda o: o.iterkeys() | ||
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# n() is useful when python3 needs a str (unicode), and python2 str (bytes) | ||
n = lambda s: s.encode('utf-8') | ||
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else: | ||
PY3 = True | ||
import builtins | ||
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# 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 | ||
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# Type aliases | ||
string_types = str, | ||
text_type = str | ||
integer_types = int, | ||
long_type = int | ||
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from io import StringIO as OutputIO | ||
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# Glue code for syntax differences | ||
def reraise(tp, value, tb=None): | ||
if value.__traceback__ is not tb: | ||
raise value.with_traceback(tb) | ||
raise value | ||
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def with_metaclass(meta, base=object): | ||
ns = dict(base=base, meta=meta) | ||
exec("""class _DjangoBase(base, metaclass=meta): | ||
pass""", ns) | ||
return ns["_DjangoBase"] | ||
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iteritems = lambda o: o.items() | ||
itervalues = lambda o: o.values() | ||
iterkeys = lambda o: o.keys() | ||
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n = lambda s: s |
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====================== | ||
Python 3 compatibility | ||
====================== | ||
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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*). | ||
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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. | ||
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* http://docs.python.org/py3k/howto/pyporting.html | ||
* http://python3porting.com/ | ||
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django.utils.py3 | ||
================ | ||
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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. | ||
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PY3 | ||
--- | ||
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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:: | ||
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from django.utils.py3 import PY3 | ||
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if PY3: | ||
# Do stuff Python 3-wise | ||
else: | ||
# Do stuff Python 2-wise | ||
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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. | ||
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String handling | ||
=============== | ||
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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:: | ||
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from __future__ import unicode_literals | ||
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my_string = "This is an unicode literal" | ||
my_bytestring = b"This is a bytestring" | ||
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Be cautious if you have to slice bytestrings. | ||
See http://docs.python.org/py3k/howto/pyporting.html#bytes-literals | ||
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Different expected strings | ||
-------------------------- | ||
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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. | ||
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>>> from __future__ import unicode_literals | ||
>>> from datetime import datetime | ||
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>>> print(datetime.date(2012, 5, 21).strftime(n("%m → %Y"))) | ||
05 → 2012 | ||
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Renamed types | ||
============= | ||
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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``. | ||
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=========== ========= ===================== | ||
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 | ||
=========== ========= ===================== | ||
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String aliases | ||
-------------- | ||
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Code sample:: | ||
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if isinstance(foo, basestring): | ||
print("foo is a string") | ||
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# I want to convert a number to a Unicode string | ||
bar = 45 | ||
bar_string = unicode(bar) | ||
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Should be replaced by:: | ||
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from django.utils.py3 import string_types, text_type | ||
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if isinstance(foo, string_types): | ||
print("foo is a string") | ||
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# I want to convert a number to a Unicode string | ||
bar = 45 | ||
bar_string = text_type(bar) | ||
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No more long type | ||
----------------- | ||
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``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: | ||
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.. code-block:: python | ||
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# Old Python 2 code | ||
my_var = long(333463247234623) | ||
if isinstance(my_var, (int, long)): | ||
# ... | ||
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Should be replaced by: | ||
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.. code-block:: python | ||
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from django.utils.py3 import long_type, integer_types | ||
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my_var = long_type(333463247234623) | ||
if isinstance(my_var, integer_types): | ||
# ... | ||
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Changed module locations | ||
======================== | ||
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The following modules have changed their location in Python 3. Therefore, it is | ||
recommended to import them from the ``django.utils.py3`` compatibility layer: | ||
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=============================== ====================================== ====================== | ||
Python 2 Python3 django.utils.py3 | ||
=============================== ====================================== ====================== | ||
Cookie http.cookies cookies | ||
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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 | ||
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htmlentitydefs.name2codepoint html.entities.name2codepoint name2codepoint | ||
HTMLParser html.parser HTMLParser | ||
cPickle/pickle pickle pickle | ||
thread/dummy_thread _thread/_dummy_thread thread | ||
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os.getcwdu os.getcwd getcwdu | ||
itertools.izip zip zip | ||
sys.maxint sys.maxsize maxsize | ||
unichr chr unichr | ||
xrange range xrange | ||
=============================== ====================================== ====================== | ||
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Ouptut encoding now Unicode | ||
=========================== | ||
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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:: | ||
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from django.utils.py3 import OutputIO | ||
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try: | ||
old_stdout = sys.stdout | ||
out = OutputIO() | ||
sys.stdout = out | ||
# Do stuff which produces standard output | ||
result = out.getvalue() | ||
finally: | ||
sys.stdout = old_stdout | ||
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Dict iteritems/itervalues/iterkeys | ||
================================== | ||
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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``:: | ||
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from django.utils.py3 import iteritems, itervalues, iterkeys | ||
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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): | ||
# ... | ||
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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. | ||
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http://docs.python.org/release/3.0.1/whatsnew/3.0.html#views-and-iterators-instead-of-lists | ||
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Metaclass | ||
========= | ||
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The syntax for declaring metaclasses has changed in Python 3. | ||
``django.utils.py3`` offers a compatible way to declare metaclasses:: | ||
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from django.utils.py3 import with_metaclass | ||
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class MyClass(with_metaclass(SubClass1, SubClass2,...)): | ||
# ... | ||
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Re-raising exceptions | ||
===================== | ||
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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:: | ||
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raise Exception, Exception(msg), traceback | ||
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Use:: | ||
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from django.utils.py3 import reraise | ||
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reraise(Exception, Exception(msg), traceback) | ||
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