Six: Python 2 and 3 Compatibility Library

Six provides simple utilities for wrapping over differences between Python 2 and Python 3.

Six can be downloaded on PyPi. Its bug tracker and code hosting is on BitBucket.

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.

Indices and tables

Package contents

six.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.

six.class_types

Possible class types. In Python 2, this encompasses old-style and new-style classes. In Python 3, this is just new-styles.

six.integer_types

Possible integer types. In Python 2, this is py2:long() and py2:int(), and in Python 3, just py3:int().

six.string_types

Possible types for text data. This is py2:basestring() in Python 2 and py3:str() in Python 3.

six.text_type

Type for representing (Unicode) textual data. This is py2:unicode() in Python 2 and py3:str() in Python 3.

six.binary_type

Type for representing binary data. This is py2:str() in Python 2 and py3:bytes() in Python 3.

six.MAXSIZE

The maximum size of a container. This is equivalent to sys.maxsize in Python 2.6 and later (including 3.x). Note, this is temptingly similar to, but not the same as py2:sys.maxint in Python 2. There is no direct equivalent to 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 intepreter data structures. The following accessors are available. Note that the recommended way to inspect functions and methods is the stdlib inspect module.

six.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)
six.get_method_function(meth)

Get the function out of method object meth.

six.get_method_self(meth)

Get the self of bound method meth.

six.get_function_code(func)

Get the code object associated with func.

six.get_function_defaults(func)

Get the defaults tuple associated with func.

six.advance_iterator(it)

Get the next item of iterator it. 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.

six.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.

six.iterkeys(dictionary)

Returns an iterator over dictionary's keys. This replaces dictionary.iterkeys() on Python 2 and dictionary.keys() on Python 3.

six.itervalues(dictionary)

Returns an iterator over dictionary's values. This replaces dictionary.itervalues() on Python 2 and dictionary.values() on Python 3.

six.iteritems(dictionary)

Returns an iterator over dictionary's items. This replaces dictionary.iteritems() on Python 2 and dictionary.items() on Python 3.

Syntax compatibility

These functions smooth over operations which have different syntaxes between Python 2 and 3.

six.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.

six.print_(*args, *, file=sys.stdout, end="\n", sep=" ")

Print args into file. Each argument will be separated with sep and end will be written to the file at the last.

Note

In Python 2, this function imitates Python 3’s print() by not having softspace support. If you don’t know what that is, you’re probably ok. :)

six.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.

six.with_metaclass(metaclass, base=object)

Create a new class with base class base 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

Binary and text data

Python 3 enforces the distinction between byte strings and text strings far more rigoriously 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.

six.b(data)

A “fake” bytes literal. data should always be a normal string literal. In Python 2, b() returns a 8-bit string. In Python 3, data is encoded with the latin-1 encoding to bytes.

six.u(text)

A “fake” unicode literal. text should always be a normal string literal. In Python 2, 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.

six.int2byte(i)

Converts i to a byte. i must be in range(0, 256). This is equivalent to py2:chr in Python 2 and bytes((i,)) in Python 3.

six.StringIO

This is an fake file object for textual data. It’s an alias for py2:StringIO.StringIO in Python 2 and io.StringIO in Python 3.

six.BytesIO

This is a fake file object for binary data. In Python 2, it’s an alias for py2:StringIO.StringIO, but in Python 3, it’s an alias for io.BytesIO.

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 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, 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 appropiate 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.

Note

The urllib, py2:urllib2, and py2:urlparse modules have been combined in the urllib package in Python 3. six.moves doesn’t not support their renaming because their members have been mixed across several modules in that package.

Supported renames:

Name

Python 2 name

Python 3 name

builtins

py2:__builtin__

builtins

configparser

py2:ConfigParser

configparser

copyreg

py2:copy_reg

copyreg

cPickle

py2:cPickle

pickle

cStringIO

py2:cStringIO.StringIO()

io.StringIO

filter

py2:itertools.ifilter()

filter()

http_cookiejar

py2:cookielib

http.cookiejar

http_cookies

py2:Cookie

http.cookies

html_entities

py2:htmlentitydefs

html.entities

html_parser

py2:HTMLParser

html.parser

http_client

py2:httplib

http.client

BaseHTTPServer

py2:BaseHTTPServer

http.server

CGIHTTPServer

py2:CGIHTTPServer

http.server

SimpleHTTPServer

py2:SimpleHTTPServer

http.server

map

py2:itertools.imap

py3:map

queue

py2:Queue

queue

reduce

py2:reduce()

functools.reduce()

reload_module

py2:reload()

py3:imp.reload()

reprlib

py2:repr

reprlib

socketserver

py2:SocketServer

socketserver

tkinter

py2:Tkinter

tkinter

tkinter_dialog

py2:Dialog

py3:tkinter.dialog

tkinter_filedialog

py2:FileDialog

py3:tkinter.FileDialog

tkinter_scrolledtext

py2:ScrolledText

py3:tkinter.scolledtext

tkinter_simpledialog

py2:SimpleDialog

tkinter.simpledialog

tkinter_tix

py2:Tix

tkinter.tix

tkinter_constants

py2:Tkconstants

py3:tkinter.constants

tkinter_dnd

py2:Tkdnd

tkinter.dnd

tkinter_colorchooser

py2:tkColorChooser

tkinter.colorchooser

tkinter_commondialog

py2:tkCommonDialog

tkinter.commondialog

tkinter_tkfiledialog

py2:tkFileDialog

tkinter.filedialog

tkinter_font

py2:tkFont

tkinter.font

tkinter_messagebox

py2:tkMessageBox

tkinter.messagebox

tkinter_tksimpledialog

py2:tkSimpleDialog

tkinter.simpledialog

urllib_robotparser

py2:robotparser

urllib.robotparser

winreg

py2:_winreg

winreg

xrange

py2:xrange()

py3:range()

zip

py2:itertools.izip()

zip()

Advanced - Customizing renames

It is possible to add additional names to the six.moves namespace.

six.add_move(item)

Add item to the six.moves mapping. item should be a MovedAttribute or MovedModule instance.

six.remove_move(name)

Remove the six.moves mapping called name. name should be a string.

Instances of the following classes can be passed to add_move(). Neither have any public members.

class six.MovedModule(name, old_mod, new_mod)

Create a mapping for 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.

class six.MovedAttribute(name, old_mod, new_mod, old_attr=None, new_attr=None)

Create a mapping for 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.