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Six: Python 2 and 3 Compatibility Library

.. 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.

Indices and tables

Package contents

.. 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.


Constants

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.


.. 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)

Object model compatibility

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 exactly the :func:`py3:functools.wraps` decorator, but it sets the
   ``__wrapped__`` attribute on what it decorates as :func:`py3:functools.wraps`
   does on Python versions after 3.2.


Syntax compatibility

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)


Binary and text data

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
   :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.


unittest assertions

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.


Renamed modules and attributes compatibility

.. 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 imp 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:

Name Python 2 name Python 3 name
builtins :mod:`py2:__builtin__` :mod:`py3:builtins`
configparser :mod:`py2:ConfigParser` :mod:`py3:configparser`
copyreg :mod:`py2:copy_reg` :mod:`py3:copyreg`
cPickle :mod:`py2:cPickle` :mod:`py3:pickle`
cStringIO :func:`py2:cStringIO.StringIO` :class:`py3:io.StringIO`
dbm_gnu :func:`py2:gdbm` :class:`py3:dbm.gnu`
_dummy_thread :mod:`py2:dummy_thread` :mod:`py3:_dummy_thread`
email_mime_base :mod:`py2:email.MIMEBase` :mod:`py3:email.mime.base`
email_mime_image :mod:`py2:email.MIMEImage` :mod:`py3:email.mime.image`
email_mime_multipart :mod:`py2:email.MIMEMultipart` :mod:`py3:email.mime.multipart`
email_mime_nonmultipart :mod:`py2:email.MIMENonMultipart` :mod:`py3:email.mime.nonmultipart`
email_mime_text :mod:`py2:email.MIMEText` :mod:`py3:email.mime.text`
filter :func:`py2:itertools.ifilter` :func:`py3:filter`
filterfalse :func:`py2:itertools.ifilterfalse` :func:`py3:itertools.filterfalse`
getcwd :func:`py2:os.getcwdu` :func:`py3:os.getcwd`
getcwdb :func:`py2:os.getcwd` :func:`py3:os.getcwdb`
getoutput :func:`py2:commands.getoutput` :func:`py3:subprocess.getoutput`
http_cookiejar :mod:`py2:cookielib` :mod:`py3:http.cookiejar`
http_cookies :mod:`py2:Cookie` :mod:`py3:http.cookies`
html_entities :mod:`py2:htmlentitydefs` :mod:`py3:html.entities`
html_parser :mod:`py2:HTMLParser` :mod:`py3:html.parser`
http_client :mod:`py2:httplib` :mod:`py3:http.client`
BaseHTTPServer :mod:`py2:BaseHTTPServer` :mod:`py3:http.server`
CGIHTTPServer :mod:`py2:CGIHTTPServer` :mod:`py3:http.server`
SimpleHTTPServer :mod:`py2:SimpleHTTPServer` :mod:`py3:http.server`
input :func:`py2:raw_input` :func:`py3:input`
intern :func:`py2:intern` :func:`py3:sys.intern`
map :func:`py2:itertools.imap` :func:`py3:map`
queue :mod:`py2:Queue` :mod:`py3:queue`
range :func:`py2:xrange` :func:`py3:range`
reduce :func:`py2:reduce` :func:`py3:functools.reduce`
reload_module :func:`py2:reload` :func:`py3:imp.reload`, :func:`py3:importlib.reload` on Python 3.4+
reprlib :mod:`py2:repr` :mod:`py3:reprlib`
shlex_quote :mod:`py2:pipes.quote` :mod:`py3:shlex.quote`
socketserver :mod:`py2:SocketServer` :mod:`py3:socketserver`
_thread :mod:`py2:thread` :mod:`py3:_thread`
tkinter :mod:`py2:Tkinter` :mod:`py3:tkinter`
tkinter_dialog :mod:`py2:Dialog` :mod:`py3:tkinter.dialog`
tkinter_filedialog :mod:`py2:FileDialog` :mod:`py3:tkinter.FileDialog`
tkinter_scrolledtext :mod:`py2:ScrolledText` :mod:`py3:tkinter.scrolledtext`
tkinter_simpledialog :mod:`py2:SimpleDialog` :mod:`py3:tkinter.simpledialog`
tkinter_ttk :mod:`py2:ttk` :mod:`py3:tkinter.ttk`
tkinter_tix :mod:`py2:Tix` :mod:`py3:tkinter.tix`
tkinter_constants :mod:`py2:Tkconstants` :mod:`py3:tkinter.constants`
tkinter_dnd :mod:`py2:Tkdnd` :mod:`py3:tkinter.dnd`
tkinter_colorchooser :mod:`py2:tkColorChooser` :mod:`py3:tkinter.colorchooser`
tkinter_commondialog :mod:`py2:tkCommonDialog` :mod:`py3:tkinter.commondialog`
tkinter_tkfiledialog :mod:`py2:tkFileDialog` :mod:`py3:tkinter.filedialog`
tkinter_font :mod:`py2:tkFont` :mod:`py3:tkinter.font`
tkinter_messagebox :mod:`py2:tkMessageBox` :mod:`py3:tkinter.messagebox`
tkinter_tksimpledialog :mod:`py2:tkSimpleDialog` :mod:`py3:tkinter.simpledialog`
urllib.parse See :mod:`six.moves.urllib.parse` :mod:`py3:urllib.parse`
urllib.error See :mod:`six.moves.urllib.error` :mod:`py3:urllib.error`
urllib.request See :mod:`six.moves.urllib.request` :mod:`py3:urllib.request`
urllib.response See :mod:`six.moves.urllib.response` :mod:`py3:urllib.response`
urllib.robotparser :mod:`py2:robotparser` :mod:`py3:urllib.robotparser`
urllib_robotparser :mod:`py2:robotparser` :mod:`py3:urllib.robotparser`
UserDict :class:`py2:UserDict.UserDict` :class:`py3:collections.UserDict`
UserList :class:`py2:UserList.UserList` :class:`py3:collections.UserList`
UserString :class:`py2:UserString.UserString` :class:`py3:collections.UserString`
winreg :mod:`py2:_winreg` :mod:`py3:winreg`
xmlrpc_client :mod:`py2:xmlrpclib` :mod:`py3:xmlrpc.client`
xmlrpc_server :mod:`py2:SimpleXMLRPCServer` :mod:`py3:xmlrpc.server`
xrange :func:`py2:xrange` :func:`py3:range`
zip :func:`py2:itertools.izip` :func:`py3:zip`
zip_longest :func:`py2:itertools.izip_longest` :func:`py3:itertools.zip_longest`

urllib parse

.. 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:

:mod:`py2:urlparse`:

and :mod:`py2:urllib`:

urllib error

.. 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:

:mod:`py2:urllib`:

and :mod:`py2:urllib2`:

urllib request

.. 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:

:mod:`py2:urllib`:

and :mod:`py2:urllib2`:

urllib response

.. 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:

:mod:`py2:urllib`:

Advanced - Customizing renames

.. 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.