Six: Python 2 and 3 Compatibility Library

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 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 by the Zope Five project.

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Package contents

six.PY2

A boolean indicating if the code is running on Python 2.

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 basestring() in Python 2 and py3:str() in Python 3.

six.text_type

Type for representing (Unicode) textual data. This is 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 like py3:list() or py3:dict(). 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 sys.maxint in Python 2. There is no direct equivalent to 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_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.

six.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.

six.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.

six.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.

six.next(it)

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, **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.

six.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.

six.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.

six.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. kwargs are passed through to the underlying method.

six.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 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.

class six.Iterator

A class for making portable iterators. The intention is that it be subclassed and subclasses provide a __next__ method. In Python 2, 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__. Iterator is empty on Python 3. (In fact, it is just aliased to object.)

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.

Note

Python 3’s exec() doesn’t take keyword arguments, so calling exec() with them should be avoided.

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 after the last argument is printed.

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, *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 add_metaclass() decorator.

six.add_metaclass(metaclass)

Class decorator that replaces a normally-constructed class with a metaclass-constructed one. Unlike with_metaclass(), add_metaclass() does not create an intermediate base class between the class being created and its bases. 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__ = MyMeta

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 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.

Note

Since all Python versions 2.6 and after support the b prefix, b(), code without 2.5 support doesn’t need b().

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.

Note

In Python 3.3, the u prefix has been reintroduced. Code that only supports Python 3 versions greater than 3.3 thus does not need u().

Note

On Python 2, 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 u() with strings of ASCII data.

six.unichr(c)

Return the (Unicode) string representing the codepoint c. This is equivalent to unichr() on Python 2 and chr() on Python 3.

six.int2byte(i)

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

six.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.

six.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.

six.iterbytes(buf)

Return an iterator over bytes in buf as integers. This is equivalent to a bytes object iterator in Python 3.

six.StringIO

This is an fake file object for textual data. It’s an alias for 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 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.

The urllib, urllib2, and urlparse modules have been combined in the urllib package in Python 3. The six.moves.urllib package is a version-independent location for this functionality; its structure mimics the structure of the Python 3 urllib package.

Supported renames:

Name	Python 2 name	Python 3 name
builtins	__builtin__	builtins
configparser	ConfigParser	configparser
copyreg	copy_reg	copyreg
cPickle	cPickle	pickle
cStringIO	cStringIO.StringIO()	io.StringIO
dbm_gnu	py2:gdbm()	py3:dbm.gnu
email_mime_multipart	py2:email.MIMEMultipart	py3:email.mime.multipart
email_mime_text	py2:email.MIMEText	py3:email.mime.text
email_mime_base	py2:email.MIMEBase	py3:email.mime.base
filter	itertools.ifilter()	filter()
filterfalse	itertools.ifilterfalse()	itertools.filterfalse()
http_cookiejar	cookielib	http.cookiejar
http_cookies	Cookie	http.cookies
html_entities	htmlentitydefs	html.entities
html_parser	HTMLParser	html.parser
http_client	httplib	http.client
BaseHTTPServer	BaseHTTPServer	http.server
CGIHTTPServer	CGIHTTPServer	http.server
SimpleHTTPServer	SimpleHTTPServer	http.server
input	raw_input()	input()
map	itertools.imap()	map()
queue	Queue	queue
range	xrange()	py3:range()
reduce	reduce()	functools.reduce()
reload_module	reload()	py3:imp.reload()
reprlib	py2:repr	reprlib
socketserver	SocketServer	socketserver
_thread	thread	_thread
tkinter	Tkinter	tkinter
tkinter_dialog	py2:Dialog	py3:tkinter.dialog
tkinter_filedialog	py2:FileDialog	py3:tkinter.FileDialog
tkinter_scrolledtext	ScrolledText	tkinter.scrolledtext
tkinter_simpledialog	py2:SimpleDialog	tkinter.simpledialog
tkinter_ttk	ttk	tkinter.ttk
tkinter_tix	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.parse	See six.moves.urllib.parse	urllib.parse
urllib.error	See six.moves.urllib.error	urllib.error
urllib.request	See six.moves.urllib.request	urllib.request
urllib.response	See six.moves.urllib.response	urllib.response
urllib.robotparser	robotparser	urllib.robotparser
urllib_robotparser	robotparser	urllib.robotparser
UserString	UserString.UserString	collections.UserString
winreg	_winreg	winreg
xmlrpc_client	xmlrpclib	py3:xmlrpclib
xrange	xrange()	py3:range()
zip	itertools.izip()	zip()
zip_longest	itertools.izip_longest()	itertools.zip_longest()

urllib parse

Contains functions from Python 3’s urllib.parse and Python 2’s:

urlparse:

• py2:urlparse.ParseResult()

• urlparse.urlparse()

• urlparse.urlunparse()

• urlparse.parse_qs()

• urlparse.parse_qsl()

• urlparse.urljoin()

• urlparse.urldefrag()

• urlparse.urlsplit()

• urlparse.urlunsplit()

and urllib:

• urllib.quote()

• urllib.quote_plus()

• urllib.unquote()

• urllib.unquote_plus()

• urllib.urlencode()

urllib error

Contains exceptions from Python 3’s urllib.error and Python 2’s:

urllib:

• urllib.ContentTooShortError

and urllib2:

• urllib2.URLError

• urllib2.HTTPError

urllib request

Contains items from Python 3’s urllib.request and Python 2’s:

urllib:

• urllib.pathname2url()

• urllib.url2pathname()

• urllib.getproxies()

• urllib.urlretrieve()

• urllib.urlcleanup()

• urllib.URLopener

• urllib.FancyURLopener

• py2:urllib.proxy_bypass()

and urllib2:

• urllib2.urlopen()

• urllib2.install_opener()

• urllib2.build_opener()

• urllib2.Request

• urllib2.OpenerDirector

• urllib2.HTTPDefaultErrorHandler

• urllib2.HTTPRedirectHandler

• urllib2.HTTPCookieProcessor

• urllib2.ProxyHandler

• urllib2.BaseHandler

• urllib2.HTTPPasswordMgr

• urllib2.HTTPPasswordMgrWithDefaultRealm

• urllib2.AbstractBasicAuthHandler

• urllib2.HTTPBasicAuthHandler

• urllib2.ProxyBasicAuthHandler

• urllib2.AbstractDigestAuthHandler

• urllib2.HTTPDigestAuthHandler

• urllib2.ProxyDigestAuthHandler

• urllib2.HTTPHandler

• urllib2.HTTPSHandler

• urllib2.FileHandler

• urllib2.FTPHandler

• urllib2.CacheFTPHandler

• urllib2.UnknownHandler

• urllib2.HTTPErrorProcessor

urllib response

Contains classes from Python 3’s urllib.response and Python 2’s:

urllib:

• py2:urllib.addbase

• py2:urllib.addclosehook

• py2:urllib.addinfo

• py2:urllib.addinfourl

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.