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Add Python 3 support to Python 2 applications using the six module.

Project description

sixer is a tool adding Python 3 support to a Python 2 project. It was written to produces patches to port OpenStack to Python 3. It is focused on supporting Python 2.7 and 3.4.

It uses basic regular expressions to find code which needs to be modified. It emits warnings when code was not patched or looks suspicious.

See also the six module documentation.

Usage [--write] [options] <all|operation1[,operation2,...]> <directories or filenames> displays the name of patched files. It displays warnings for suspicious code which may have to be ported manually.

The first parameter can be a list of operations separated by commas. Use "all" to apply all operations. Operation prefixed by - are excluded. For example, "all,-iteritems" applies all operations except iteritems.

For directories, searchs for .py files in all subdirectories.

By default, sixer uses a dry run: files are not modified. Add --write (or -w) option to modify files in place. It’s better to use sixer in a project managed by a source control manager (ex: git) to see differences and revert unwanted changes. The original files are not kept.

Use --help to see all available options.

See below for the list of available operations.


  • all:

    • combine all operations all together

  • basestring:

    • replace basestring with six.string_types

  • dict0:

    • replace dict.keys()[0] with list(dict.keys())[0]

    • same for dict.values()[0] and dict.items()[0]

  • dict_add:

    • replace dict.keys() + list2 with list(dict.keys()) + list2

    • same for dict.values() + list2 and dict.items() + list2

  • except:

    • Replace except ValueError, exc: with except ValueError as exc:

    • Replace except (TypeError, ValueError), exc: with except (TypeError, ValueError) as exc:

  • iteritems:

    • replace dict.iteritems() with six.iteritems(dict)

  • itervalues:

    • replace dict.itervalues() with six.itervalues(dict)

  • iterkeys:

    • replace dict.iterkeys() with six.iterkeys(dict)

    • note: for key in dict.iterkeys(): can usually be simplified to for key in dict:

  • itertools:

    • replace itertools.ifilter with six.moves.filter

    • similar change for ifilterfalse(), imap(), izip() and izip_longest() of the itertools module

  • long:

    • replace 123L with 123

    • replace (int, long) with six.integer_types

    • octal number are unchanged (ex: 010L)

  • next:

    • replace with next(iter)

  • raise:

    • replace raise exc[0], exc[1], exc[2] with six.reraise(*exc)

    • replace raise exc_type, exc_value, exc_tb with six.reraise(exc_type, exc_value, exc_tb)

    • replace raise exc, msg with raise exc(msg)

  • six_moves:

    • replace Python 2 imports with imports from six.moves. Python 2 modules:

      • BaseHTTPServer

      • ConfigParser

      • Cookie

      • HTMLParser

      • Queue

      • SimpleHTTPServer

      • SimpleXMLRPCServer

      • __builtin__

      • cPickle

      • cookielib

      • htmlentitydefs

      • httplib

      • repr

      • xmlrpclib

    • replace Python 2 functions with six.moves.<function>. Python 2 functions:

      • raw_input()

      • reduce()

      • reload()

    • replace unichr() with six.unichr()

  • urllib:

    • replace Python 2 urllib and urllib2 with six.moves.urllib

  • stringio:

    • replace StringIO.StringIO with six.StringIO

    • replace cStringIO.StringIO with moves.cStringIO

    • replace from StringIO import StringIO with from six import StringIO

    • replace from cStringIO import StringIO with from six.moves import cStringIO as StringIO

    • later you may have to replace it with six.BytesIO (or io.BytesIO if you don’t support Python 2.6) when bytes are expected on Python 3

  • unicode:

    • replace unicode with six.text_type

    • replace (str, unicode) with six.string_types

  • xrange:

    • replace xrange() with range() and add from six.moves import range

    • don’t add the import if all ranges have 1024 items or less


To install sixer, type:

pip3 install sixer

sixer requires Python 3, it doesn’t work on Python 2.

Adding the six import

When an operation uses six, import six may be added. sixer repects OpenStack coding style rules to add the import: imports grouped by standard library, third party and application imports; and imports must be are sorted.


Since the project is implemented with regular expressions, it can produce false positives (invalid changes). For example, some operations replace patterns in strings, comments or function names even if it doesn’t make sense.

Try also the 2to6 project which may be more reliable.


To run tests, type tox. Type pip install -U tox to install or update the tox program.

Or run tests manually: type python3

Resources to port code to Python 3


  • Version 1.0 (2015-10-16)

  • sixer doesn’t modify files by default anymore. Add --write to really modify files inplace.

  • long operation now also replaces (int, long) with six.integer_types

  • itertools now also replaces ifilterfalse(), izip() and izip_longest() of the itertools module

  • six_moves now also replaces unichr(ch) with six.unichr(ch)

  • command line: it’s now possible to exclude an operation using - prefix. For example, all,-iteritems applies all operations except iteritems.

  • Version 0.8 (2015-10-03)

  • urllib now emits a warning on unknown symbol, instead of raising an exception

  • Write warnings to stderr instead of stdout and exit with error code 1 if a filename doesn’t exist or a directory doesn’t contain any .py file

  • unicode operation also replaces (str, unicode) with six.string_types

  • When removing an import, don’t remove the empty line following the import if the empty line is followed by a second import

  • long also replaces 1l (lower case L suffix for long numbers)

  • Version 0.7 (2015-09-29)

  • Add new dict0, dict_add and except operations

  • Add –app command line option to specify the Python module of the application, to help sorting imports

  • Code adding new imports respect better OpenStack coding style on imports. For example, it adds two empty lines after imports, instead of a single line.

  • Display the name of the operation which modified files

  • Display also the name of the operation in warnings

  • six_moves now also patches reduce() and reload(). For example, reduce() is replaced with six.moves.reduce().

  • six_moves now also patches mock.patch(). For example, with mock.patch(''): ... is replaced with with mock.patch(''): ...

  • urllib now also replaces from ... import ... imports. For example, from urllib import quote is replaced with from six.moves.urllib.parse import quote.

  • Version 0.6 (2015-09-11)

  • Add “itertools” operation

  • Fix xrange() regex to not modify “from six.moves import xrange” and “moves.xrange(n)”

  • Fix urllib for urllib or urlparse module get from the urllib2 module. For example, urllib2.urlparse.urlparse (import urllib2) is now replaced with urllib.parse.urlparse (from six.moves import urllib).

  • Version 0.5 (2015-07-08)

  • six_moves: support “import module as name” syntax and add cPickle module

  • Add –to-stdout, –quiet and –max-range command line options

  • Emit a warning if the directory does not contain any .py file or if the path does not exist

  • Test also directly the program

  • Version 0.4 (2015-06-09)

  • now accepts multiple filenames on the command line, but operations becomes the first command line parameter

  • the stringio operation now also replaces cStringIO and from StringIO import StringIO

  • urllib: replace also urlparse.symbol

  • six_moves: support more modules: Cookie, HTMLParser, SimpleHTTPServer, cookielib, xmlrpclib, etc.

  • Refactor operations as classes to cleanup the code

  • Version 0.3.1 (2015-05-27)

  • Fix the “all” operation

  • six_moves knows more modules

  • urllib: add pathname2url, don’t touch urllib2.parse_http_list()

  • Version 0.3 (2015-05-27)

  • First command line parameter can now be a filename

  • Add “all”, “basestring”, “iterkeys”, “six_moves”, “stringio” and “urllib” operations

  • Enhance the knownledge tables for modules (stdlib, third parties, applications)

  • Ignore unparsable import lines when adding an import

  • Version 0.2 (2015-05-12):

  • First public release

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