.. module:: six :synopsis: Python 2 and 3 compatibility
.. moduleauthor:: Benjamin Peterson <benjamin@python.org>
.. sectionauthor:: Benjamin Peterson <benjamin@python.org>
Six provides simple utilities for wrapping over differences between Python 2 and Python 3. It is intended to support codebases that work on both Python 2 and 3 without modification. six consists of only one Python file, so it is painless to copy into a project.
Six can be downloaded on PyPI. Its bug tracker and code hosting is on GitHub.
The name, "six", comes from the fact that 2*3 equals 6. Why not addition? Multiplication is more powerful, and, anyway, "five" has already been snatched away by the (admittedly now moribund) Zope Five project.
.. data:: PY2 A boolean indicating if the code is running on Python 2.
.. data:: PY3 A boolean indicating if the code is running on Python 3.
Six provides constants that may differ between Python versions. Ones ending
_types are mostly useful as the second argument to isinstance or
issubclass.
.. data:: class_types Possible class types. In Python 2, this encompasses old-style :data:`py2:types.ClassType` and new-style ``type`` classes. In Python 3, this is just ``type``.
.. data:: integer_types Possible integer types. In Python 2, this is :func:`py2:long` and :func:`py2:int`, and in Python 3, just :func:`py3:int`.
.. data:: string_types Possible types for text data. This is :func:`py2:basestring` in Python 2 and :func:`py3:str` in Python 3.
.. data:: text_type Type for representing (Unicode) textual data. This is :func:`py2:unicode` in Python 2 and :func:`py3:str` in Python 3.
.. data:: binary_type Type for representing binary data. This is :func:`py2:str` in Python 2 and :func:`py3:bytes` in Python 3. Python 2.6 and 2.7 include ``bytes`` as a builtin alias of ``str``, so six’s version is only necessary for Python 2.5 compatibility.
.. data:: MAXSIZE The maximum size of a container like :func:`py3:list` or :func:`py3:dict`. This is equivalent to :data:`py3:sys.maxsize` in Python 2.6 and later (including 3.x). Note, this is temptingly similar to, but not the same as :data:`py2:sys.maxint` in Python 2. There is no direct equivalent to :data:`py2:sys.maxint` in Python 3 because its integer type has no limits aside from memory.
Here's example usage of the module:
import six
def dispatch_types(value):
if isinstance(value, six.integer_types):
handle_integer(value)
elif isinstance(value, six.class_types):
handle_class(value)
elif isinstance(value, six.string_types):
handle_string(value)
Python 3 renamed the attributes of several interpreter data structures. The following accessors are available. Note that the recommended way to inspect functions and methods is the stdlib :mod:`py3:inspect` module.
.. function:: get_unbound_function(meth)
Get the function out of unbound method *meth*. In Python 3, unbound methods
don't exist, so this function just returns *meth* unchanged. Example
usage::
from six import get_unbound_function
class X(object):
def method(self):
pass
method_function = get_unbound_function(X.method)
.. function:: get_method_function(meth) Get the function out of method object *meth*.
.. function:: get_method_self(meth) Get the ``self`` of bound method *meth*.
.. function:: get_function_closure(func) Get the closure (list of cells) associated with *func*. This is equivalent to ``func.__closure__`` on Python 2.6+ and ``func.func_closure`` on Python 2.5.
.. function:: get_function_code(func) Get the code object associated with *func*. This is equivalent to ``func.__code__`` on Python 2.6+ and ``func.func_code`` on Python 2.5.
.. function:: get_function_defaults(func) Get the defaults tuple associated with *func*. This is equivalent to ``func.__defaults__`` on Python 2.6+ and ``func.func_defaults`` on Python 2.5.
.. function:: get_function_globals(func) Get the globals of *func*. This is equivalent to ``func.__globals__`` on Python 2.6+ and ``func.func_globals`` on Python 2.5.
.. function:: next(it)
advance_iterator(it)
Get the next item of iterator *it*. :exc:`py3:StopIteration` is raised if
the iterator is exhausted. This is a replacement for calling ``it.next()``
in Python 2 and ``next(it)`` in Python 3. Python 2.6 and above have a
builtin ``next`` function, so six's version is only necessary for Python 2.5
compatibility.
.. function:: callable(obj) Check if *obj* can be called. Note ``callable`` has returned in Python 3.2, so using six's version is only necessary when supporting Python 3.0 or 3.1.
.. function:: iterkeys(dictionary, **kwargs) Returns an iterator over *dictionary*\'s keys. This replaces ``dictionary.iterkeys()`` on Python 2 and ``dictionary.keys()`` on Python 3. *kwargs* are passed through to the underlying method.
.. function:: itervalues(dictionary, **kwargs) Returns an iterator over *dictionary*\'s values. This replaces ``dictionary.itervalues()`` on Python 2 and ``dictionary.values()`` on Python 3. *kwargs* are passed through to the underlying method.
.. function:: iteritems(dictionary, **kwargs) Returns an iterator over *dictionary*\'s items. This replaces ``dictionary.iteritems()`` on Python 2 and ``dictionary.items()`` on Python 3. *kwargs* are passed through to the underlying method.
.. function:: iterlists(dictionary, **kwargs) Calls ``dictionary.iterlists()`` on Python 2 and ``dictionary.lists()`` on Python 3. No builtin Python mapping type has such a method; this method is intended for use with multi-valued dictionaries like `Werkzeug's <http://werkzeug.pocoo.org/docs/datastructures/#werkzeug.datastructures.MultiDict>`_. *kwargs* are passed through to the underlying method.
.. function:: viewkeys(dictionary) Return a view over *dictionary*\'s keys. This replaces :meth:`py2:dict.viewkeys` on Python 2.7 and :meth:`py3:dict.keys` on Python 3.
.. function:: viewvalues(dictionary) Return a view over *dictionary*\'s values. This replaces :meth:`py2:dict.viewvalues` on Python 2.7 and :meth:`py3:dict.values` on Python 3.
.. function:: viewitems(dictionary) Return a view over *dictionary*\'s items. This replaces :meth:`py2:dict.viewitems` on Python 2.7 and :meth:`py3:dict.items` on Python 3.
.. function:: create_bound_method(func, obj) Return a method object wrapping *func* and bound to *obj*. On both Python 2 and 3, this will return a :func:`py3:types.MethodType` object. The reason this wrapper exists is that on Python 2, the ``MethodType`` constructor requires the *obj*'s class to be passed.
.. function:: create_unbound_method(func, cls) Return an unbound method object wrapping *func*. In Python 2, this will return a :func:`py2:types.MethodType` object. In Python 3, unbound methods do not exist and this wrapper will simply return *func*.
A class for making portable iterators. The intention is that it be subclassed
and subclasses provide a __next__ method. In Python 2, :class:`Iterator`
has one method: next. It simply delegates to __next__. An alternate
way to do this would be to simply alias next to __next__. However,
this interacts badly with subclasses that override
__next__. :class:`Iterator` is empty on Python 3. (In fact, it is just
aliased to :class:`py3:object`.)
.. decorator:: wraps(wrapped, assigned=functools.WRAPPER_ASSIGNMENTS, updated=functools.WRAPPER_UPDATES) This is Python 3.2's :func:`py3:functools.wraps` decorator. It sets the ``__wrapped__`` attribute on what it decorates. It doesn't raise an error if any of the attributes mentioned in ``assigned`` and ``updated`` are missing on ``wrapped`` object.
These functions smooth over operations which have different syntaxes between Python 2 and 3.
.. function:: exec_(code, globals=None, locals=None)
Execute *code* in the scope of *globals* and *locals*. *code* can be a
string or a code object. If *globals* or *locals* are not given, they will
default to the scope of the caller. If just *globals* is given, it will also
be used as *locals*.
.. note::
Python 3's :func:`py3:exec` doesn't take keyword arguments, so calling
:func:`exec` with them should be avoided.
.. function:: print_(*args, *, file=sys.stdout, end="\\n", sep=" ", flush=False)
Print *args* into *file*. Each argument will be separated with *sep* and
*end* will be written to the file after the last argument is printed. If
*flush* is true, ``file.flush()`` will be called after all data is written.
.. note::
In Python 2, this function imitates Python 3's :func:`py3:print` by not
having softspace support. If you don't know what that is, you're probably
ok. :)
.. function:: raise_from(exc_value, exc_value_from) Raise an exception from a context. On Python 3, this is equivalent to ``raise exc_value from exc_value_from``. On Python 2, which does not support exception chaining, it is equivalent to ``raise exc_value``.
.. function:: reraise(exc_type, exc_value, exc_traceback=None) Reraise an exception, possibly with a different traceback. In the simple case, ``reraise(*sys.exc_info())`` with an active exception (in an except block) reraises the current exception with the last traceback. A different traceback can be specified with the *exc_traceback* parameter. Note that since the exception reraising is done within the :func:`reraise` function, Python will attach the call frame of :func:`reraise` to whatever traceback is raised.
.. function:: with_metaclass(metaclass, *bases)
Create a new class with base classes *bases* and metaclass *metaclass*. This
is designed to be used in class declarations like this: ::
from six import with_metaclass
class Meta(type):
pass
class Base(object):
pass
class MyClass(with_metaclass(Meta, Base)):
pass
Another way to set a metaclass on a class is with the :func:`add_metaclass`
decorator.
.. decorator:: add_metaclass(metaclass)
Class decorator that replaces a normally-constructed class with a
metaclass-constructed one. Example usage: ::
@add_metaclass(Meta)
class MyClass(object):
pass
That code produces a class equivalent to ::
class MyClass(object, metaclass=Meta):
pass
on Python 3 or ::
class MyClass(object):
__metaclass__ = Meta
on Python 2.
Note that class decorators require Python 2.6. However, the effect of the
decorator can be emulated on Python 2.5 like so::
class MyClass(object):
pass
MyClass = add_metaclass(Meta)(MyClass)
Python 3 enforces the distinction between byte strings and text strings far more rigorously than Python 2 does; binary data cannot be automatically coerced to or from text data. six provides several functions to assist in classifying string data in all Python versions.
.. function:: b(data)
A "fake" bytes literal. *data* should always be a normal string literal. In
Python 2, :func:`b` returns an 8-bit string. In Python 3, *data* is encoded
with the latin-1 encoding to bytes.
.. note::
Since all Python versions 2.6 and after support the ``b`` prefix,
code without 2.5 support doesn't need :func:`b`.
.. function:: u(text)
A "fake" unicode literal. *text* should always be a normal string literal.
In Python 2, :func:`u` returns unicode, and in Python 3, a string. Also, in
Python 2, the string is decoded with the ``unicode-escape`` codec, which
allows unicode escapes to be used in it.
.. note::
In Python 3.3, the ``u`` prefix has been reintroduced. Code that only
supports Python 3 versions of 3.3 and higher thus does not need
:func:`u`.
.. note::
On Python 2, :func:`u` doesn't know what the encoding of the literal
is. Each byte is converted directly to the unicode codepoint of the same
value. Because of this, it's only safe to use :func:`u` with strings of
ASCII data.
.. function:: unichr(c) Return the (Unicode) string representing the codepoint *c*. This is equivalent to :func:`py2:unichr` on Python 2 and :func:`py3:chr` on Python 3.
.. function:: int2byte(i) Converts *i* to a byte. *i* must be in ``range(0, 256)``. This is equivalent to :func:`py2:chr` in Python 2 and ``bytes((i,))`` in Python 3.
.. function:: byte2int(bs) Converts the first byte of *bs* to an integer. This is equivalent to ``ord(bs[0])`` on Python 2 and ``bs[0]`` on Python 3.
.. function:: indexbytes(buf, i) Return the byte at index *i* of *buf* as an integer. This is equivalent to indexing a bytes object in Python 3.
.. function:: iterbytes(buf) Return an iterator over bytes in *buf* as integers. This is equivalent to a bytes object iterator in Python 3.
.. function:: ensure_binary(s, encoding='utf-8', errors='strict') Coerce *s* to :data:`binary_type`. *encoding*, *errors* are the same as :meth:`py3:str.encode`
.. function:: ensure_str(s, encoding='utf-8', errors='strict') Coerce *s* to ``str``. *encoding*, *errors* are the same as :meth:`py3:str.encode`
.. function:: ensure_text(s, encoding='utf-8', errors='strict') Coerce *s* to :data:`text_type`. *encoding*, *errors* are the same as :meth:`py3:str.encode`
.. data:: StringIO This is a fake file object for textual data. It's an alias for :class:`py2:StringIO.StringIO` in Python 2 and :class:`py3:io.StringIO` in Python 3.
.. data:: BytesIO This is a fake file object for binary data. In Python 2, it's an alias for :class:`py2:StringIO.StringIO`, but in Python 3, it's an alias for :class:`py3:io.BytesIO`.
.. decorator:: python_2_unicode_compatible A class decorator that takes a class defining a ``__str__`` method. On Python 3, the decorator does nothing. On Python 2, it aliases the ``__str__`` method to ``__unicode__`` and creates a new ``__str__`` method that returns the result of ``__unicode__()`` encoded with UTF-8.
Six contains compatibility shims for unittest assertions that have been renamed. The parameters are the same as their aliases, but you must pass the test method as the first argument. For example:
import six
import unittest
class TestAssertCountEqual(unittest.TestCase):
def test(self):
six.assertCountEqual(self, (1, 2), [2, 1])
Note these functions are only available on Python 2.7 or later.
.. function:: assertCountEqual() Alias for :meth:`~py3:unittest.TestCase.assertCountEqual` on Python 3 and :meth:`~py2:unittest.TestCase.assertItemsEqual` on Python 2.
.. function:: assertRaisesRegex() Alias for :meth:`~py3:unittest.TestCase.assertRaisesRegex` on Python 3 and :meth:`~py2:unittest.TestCase.assertRaisesRegexp` on Python 2.
.. function:: assertRegex() Alias for :meth:`~py3:unittest.TestCase.assertRegex` on Python 3 and :meth:`~py2:unittest.TestCase.assertRegexpMatches` on Python 2.
.. function:: assertNotRegex() Alias for :meth:`~py3:unittest.TestCase.assertNotRegex` on Python 3 and :meth:`~py2:unittest.TestCase.assertNotRegexpMatches` on Python 2.
.. module:: six.moves :synopsis: Renamed modules and attributes compatibility
Python 3 reorganized the standard library and moved several functions to different modules. Six provides a consistent interface to them through the fake :mod:`six.moves` module. For example, to load the module for parsing HTML on Python 2 or 3, write:
from six.moves import html_parser
Similarly, to get the function to reload modules, which was moved from the
builtin module to the importlib module, use:
from six.moves import reload_module
For the most part, :mod:`six.moves` aliases are the names of the modules in
Python 3. When the new Python 3 name is a package, the components of the name
are separated by underscores. For example, html.parser becomes
html_parser. In some cases where several modules have been combined, the
Python 2 name is retained. This is so the appropriate modules can be found when
running on Python 2. For example, BaseHTTPServer which is in
http.server in Python 3 is aliased as BaseHTTPServer.
Some modules which had two implementations have been merged in Python 3. For
example, cPickle no longer exists in Python 3; it was merged with
pickle. In these cases, fetching the fast version will load the fast one on
Python 2 and the merged module in Python 3.
The :mod:`py2:urllib`, :mod:`py2:urllib2`, and :mod:`py2:urlparse` modules have been combined in the :mod:`py3:urllib` package in Python 3. The :mod:`six.moves.urllib` package is a version-independent location for this functionality; its structure mimics the structure of the Python 3 :mod:`py3:urllib` package.
Note
In order to make imports of the form:
from six.moves.cPickle import loads
work, six places special proxy objects in :data:`py3:sys.modules`. These
proxies lazily load the underlying module when an attribute is fetched. This
will fail if the underlying module is not available in the Python
interpreter. For example, sys.modules["six.moves.winreg"].LoadKey would
fail on any non-Windows platform. Unfortunately, some applications try to
load attributes on every module in :data:`py3:sys.modules`. six mitigates
this problem for some applications by pretending attributes on unimportable
modules do not exist. This hack does not work in every case, though. If you are
encountering problems with the lazy modules and don't use any from imports
directly from six.moves modules, you can workaround the issue by removing
the six proxy modules:
d = [name for name in sys.modules if name.startswith("six.moves.")]
for name in d:
del sys.modules[name]
Supported renames:
.. module:: six.moves.urllib.parse :synopsis: Stuff from :mod:`py2:urlparse` and :mod:`py2:urllib` in Python 2 and :mod:`py3:urllib.parse` in Python 3
Contains functions from Python 3's :mod:`py3:urllib.parse` and Python 2's:
- :func:`py2:urlparse.ParseResult`
- :func:`py2:urlparse.SplitResult`
- :func:`py2:urlparse.urlparse`
- :func:`py2:urlparse.urlunparse`
- :func:`py2:urlparse.parse_qs`
- :func:`py2:urlparse.parse_qsl`
- :func:`py2:urlparse.urljoin`
- :func:`py2:urlparse.urldefrag`
- :func:`py2:urlparse.urlsplit`
- :func:`py2:urlparse.urlunsplit`
- :func:`py2:urlparse.splitquery`
- :func:`py2:urlparse.uses_fragment`
- :func:`py2:urlparse.uses_netloc`
- :func:`py2:urlparse.uses_params`
- :func:`py2:urlparse.uses_query`
- :func:`py2:urlparse.uses_relative`
and :mod:`py2:urllib`:
- :func:`py2:urllib.quote`
- :func:`py2:urllib.quote_plus`
- :func:`py2:urllib.splittag`
- :func:`py2:urllib.splituser`
- :func:`py2:urllib.splitvalue`
- :func:`py2:urllib.unquote` (also exposed as :func:`py3:urllib.parse.unquote_to_bytes`)
- :func:`py2:urllib.unquote_plus`
- :func:`py2:urllib.urlencode`
.. module:: six.moves.urllib.error :synopsis: Stuff from :mod:`py2:urllib` and :mod:`py2:urllib2` in Python 2 and :mod:`py3:urllib.error` in Python 3
Contains exceptions from Python 3's :mod:`py3:urllib.error` and Python 2's:
and :mod:`py2:urllib2`:
.. module:: six.moves.urllib.request :synopsis: Stuff from :mod:`py2:urllib` and :mod:`py2:urllib2` in Python 2 and :mod:`py3:urllib.request` in Python 3
Contains items from Python 3's :mod:`py3:urllib.request` and Python 2's:
- :func:`py2:urllib.pathname2url`
- :func:`py2:urllib.url2pathname`
- :func:`py2:urllib.getproxies`
- :func:`py2:urllib.urlretrieve`
- :func:`py2:urllib.urlcleanup`
- :class:`py2:urllib.URLopener`
- :class:`py2:urllib.FancyURLopener`
- :func:`py2:urllib.proxy_bypass`
and :mod:`py2:urllib2`:
- :func:`py2:urllib2.urlopen`
- :func:`py2:urllib2.install_opener`
- :func:`py2:urllib2.build_opener`
- :func:`py2:urllib2.parse_http_list`
- :func:`py2:urllib2.parse_keqv_list`
- :class:`py2:urllib2.Request`
- :class:`py2:urllib2.OpenerDirector`
- :class:`py2:urllib2.HTTPDefaultErrorHandler`
- :class:`py2:urllib2.HTTPRedirectHandler`
- :class:`py2:urllib2.HTTPCookieProcessor`
- :class:`py2:urllib2.ProxyHandler`
- :class:`py2:urllib2.BaseHandler`
- :class:`py2:urllib2.HTTPPasswordMgr`
- :class:`py2:urllib2.HTTPPasswordMgrWithDefaultRealm`
- :class:`py2:urllib2.AbstractBasicAuthHandler`
- :class:`py2:urllib2.HTTPBasicAuthHandler`
- :class:`py2:urllib2.ProxyBasicAuthHandler`
- :class:`py2:urllib2.AbstractDigestAuthHandler`
- :class:`py2:urllib2.HTTPDigestAuthHandler`
- :class:`py2:urllib2.ProxyDigestAuthHandler`
- :class:`py2:urllib2.HTTPHandler`
- :class:`py2:urllib2.HTTPSHandler`
- :class:`py2:urllib2.FileHandler`
- :class:`py2:urllib2.FTPHandler`
- :class:`py2:urllib2.CacheFTPHandler`
- :class:`py2:urllib2.UnknownHandler`
- :class:`py2:urllib2.HTTPErrorProcessor`
.. module:: six.moves.urllib.response :synopsis: Stuff from :mod:`py2:urllib` in Python 2 and :mod:`py3:urllib.response` in Python 3
Contains classes from Python 3's :mod:`py3:urllib.response` and Python 2's:
- :class:`py2:urllib.addbase`
- :class:`py2:urllib.addclosehook`
- :class:`py2:urllib.addinfo`
- :class:`py2:urllib.addinfourl`
.. currentmodule:: six
It is possible to add additional names to the :mod:`six.moves` namespace.
.. function:: add_move(item) Add *item* to the :mod:`six.moves` mapping. *item* should be a :class:`MovedAttribute` or :class:`MovedModule` instance.
.. function:: remove_move(name) Remove the :mod:`six.moves` mapping called *name*. *name* should be a string.
Instances of the following classes can be passed to :func:`add_move`. Neither have any public members.
Create a mapping for :mod:`six.moves` called name that references different modules in Python 2 and 3. old_mod is the name of the Python 2 module. new_mod is the name of the Python 3 module.
Create a mapping for :mod:`six.moves` called name that references different attributes in Python 2 and 3. old_mod is the name of the Python 2 module. new_mod is the name of the Python 3 module. If new_attr is not given, it defaults to old_attr. If neither is given, they both default to name.