mirror of
https://github.com/django/django.git
synced 2024-11-18 07:26:04 +00:00
5e6ded2e58
Thanks Vinay Sajip for the support of his django3 branch and Alex Gaynor, kezabelle, YorikSar for the review.
253 lines
9.3 KiB
Plaintext
253 lines
9.3 KiB
Plaintext
======================
|
|
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)
|
|
|