Fixers

Fixers come in two types: Default and Opt-in. Default fixers should not break code except for corner cases, and are idempotent (applying them more than once to given source code will make no changes after the first application). Opt-in fixers are allowed to break these rules.

Python 2 code from Python 2.6 and older will be upgraded to code that is compatible with Python 2.6, 2.7, and Python 3.

If code is using a feature unique to Python 2.7, it will not be downgraded to work with Python 2.6. For example, dict.viewitems() usage will not be removed to make the code compatible with Python 2.6.

Some fixers rely on the latest release of the six project to work (see Fixers requiring six). If you wish to turn off these fixers to avoid an external dependency on six, then use the --no-six flag.

Fixers use the API defined by 2to3. For details of how this works, and how to implement your own fixers, see Extending 2to3 with your own fixers, at python3porting.com.

Default

A default fixer will be enabled when:

  • Either no -f/--fix options are used, or -f default/--fix=default is used, or the fixer is listed explicitly in an -f/--fix option; and
  • The fixer is not listed in an -x/--nofix option; and
  • For fixers that are dependent on the six project, --no-six is not specified (see Fixers requiring six).

The -x/--nofix and --no-six options always override fixers specified using -f/--fix. The --six-unicode and --future-unicode options also disable fixers that are not applicable for those options.

Fixers requiring six

The six project provides the six module which contains various tidbits in helping to support Python 2/3 code. All six-related fixers assume the latest version of six is installed.

basestring

Replaces all references to basestring() with six.string_types.

New in version 0.4.

dict_six

Fixes various methods on the dict type for getting all keys, values, or items. E.g.:

x.values()
x.itervalues()
x.viewvalues()

becomes:

list(x.values())
six.itervalues(x)
six.viewvalues(x)

Care is taken to only call list() when not in an iterating context (e.g. not the iterable for a for loop).

filter

When a call to filter is discovered, from six.moves import filter is added to the module. Wrapping the use in a call to list() is done when necessary.

imports_six

Uses six.moves to fix various renamed modules, e.g.:

import ConfigParser
ConfigParser.ConfigParser()

becomes:

import six.moves.configparser
six.moves.configparser.ConfigParser()

The modules in Python 2 whose renaming in Python 3 is supported are:

  • __builtin__
  • _winreg
  • BaseHTTPServer
  • CGIHTTPServer
  • ConfigParser
  • copy_reg
  • Cookie
  • cookielib
  • cPickle
  • Dialog
  • dummy_thread
  • FileDialog
  • gdbm
  • htmlentitydefs
  • HTMLParser
  • httplib
  • Queue
  • repr
  • robotparser
  • ScrolledText
  • SimpleDialog
  • SimpleHTTPServer
  • SimpleXMLRPCServer
  • SocketServer
  • thread
  • Tix
  • tkColorChooser
  • tkCommonDialog
  • Tkconstants
  • Tkdnd
  • tkFileDialog
  • tkFont
  • Tkinter
  • tkMessageBox
  • tkSimpleDialog
  • ttk
  • xmlrpclib

New in version 0.4.

input_six

Changes:

input(x)
raw_input(x)

to:

from six.moves import input
eval(input(x))
input(x)

New in version 0.4.

int_long_tuple

Changes (int, long) or (long, int) to six.integer_types.

New in version 0.4.

map

If a call to map is discovered, from six.moves import map is added to the module. Wrapping the use in a call to list() is done when necessary.

metaclass

Changes:

class Foo:
    __metaclass__ = Meta

to:

import six
class Foo(six.with_metaclass(Meta)):
    pass
raise_six

Changes raise E, V, T to six.reraise(E, V, T).

unicode_type

Changes all reference of unicode to six.text_type.

xrange_six

Changes:

w = xrange(x)
y = range(z)

to:

from six.moves import range
w = range(x)
y = list(range(z))

Care is taken not to call list() when range() is used in an iterating context.

zip

If zip is called, from six.moves import zip is added to the module. Wrapping the use in a call to list() is done when necessary.

2to3 fixers

Some fixers from lib2to3 in Python’s standard library are run by default unmodified as their transformations are Python 2 compatible.

Fixers with no dependencies

file

Changes all calls to file to open.

New in version 0.4.

import

Changes implicit relative imports to explicit relative imports and adds from __future__ import absolute_import.

New in version 0.4.

next

Changes all method calls to x.next() to next(x).

print

Changes all usage of the print statement to use the print() function and adds from __future__ import print_function.

raise

Changes comma-based raise statements from:

raise E, V
raise (((E, E1), E2), E3), V

to:

raise E(V)
raise E(V)

Opt-in

To specify an opt-in fixer while also running all the default fixers, make sure to specify the -f default or --fix=default option, e.g.:

python-modernize -f default -f libmodernize.fixes.fix_open
classic_division

When a use of the division operator – / – is found, add from __future__ import division and change the operator to //. If from __future__ import division is already present, this fixer is skipped.

This is intended for use in programs where / is conventionally only used for integer division, or where it is intended to do a manual pass after running python-modernize to look for cases that should not have been changed to //. The results of division on non-integers may differ after running this fixer: for example, 3.5 / 2 == 1.75, but 3.5 // 2 == 1.0.

Some objects may override the __div__ method for a use other than division, and thus would break when changed to use a __floordiv__ method instead.

This fixer is opt-in because it may change the meaning of code as described above.

New in version 1.0.

open

When a call to open is discovered, add from io import open at the top of the module so as to use io.open() instead. This fixer is opt-in because it changes what object is returned by a call to open().

New in version 0.4.