3 2to3 - Automated Python 2 to 3 code translation
4 ===============================================
6 .. sectionauthor:: Benjamin Peterson <benjamin@python.org>
8 2to3 is a Python program that reads Python 2.x source code and applies a series
9 of *fixers* to transform it into valid Python 3.x code. The standard library
10 contains a rich set of fixers that will handle almost all code. 2to3 supporting
11 library :mod:`lib2to3` is, however, a flexible and generic library, so it is
12 possible to write your own fixers for 2to3. :mod:`lib2to3` could also be
13 adapted to custom applications in which Python code needs to be edited
22 2to3 will usually be installed with the Python interpreter as a script. It is
23 also located in the :file:`Tools/scripts` directory of the Python root.
25 2to3's basic arguments are a list of files or directories to transform. The
26 directories are to recursively traversed for Python sources.
28 Here is a sample Python 2.x source file, :file:`example.py`::
31 print "Hello, {0}!".format(name)
32 print "What's your name?"
36 It can be converted to Python 3.x code via 2to3 on the command line::
40 A diff against the original source file is printed. 2to3 can also write the
41 needed modifications right back to the source file. (A backup of the original
42 file is made unless :option:`-n` is also given.) Writing the changes back is
43 enabled with the :option:`-w` flag::
47 After transformation, :file:`example.py` looks like this::
50 print("Hello, {0}!".format(name))
51 print("What's your name?")
55 Comments and exact indentation are preserved throughout the translation process.
57 By default, 2to3 runs a set of :ref:`predefined fixers <2to3-fixers>`. The
58 :option:`-l` flag lists all available fixers. An explicit set of fixers to run
59 can be given with :option:`-f`. Likewise the :option:`-x` explicitly disables a
60 fixer. The following example runs only the ``imports`` and ``has_key`` fixers::
62 $ 2to3 -f imports -f has_key example.py
64 This command runs every fixer except the ``apply`` fixer::
66 $ 2to3 -x apply example.py
68 Some fixers are *explicit*, meaning they aren't run by default and must be
69 listed on the command line to be run. Here, in addition to the default fixers,
70 the ``idioms`` fixer is run::
72 $ 2to3 -f all -f idioms example.py
74 Notice how passing ``all`` enables all default fixers.
76 Sometimes 2to3 will find a place in your source code that needs to be changed,
77 but 2to3 cannot fix automatically. In this case, 2to3 will print a warning
78 beneath the diff for a file. You should address the warning in order to have
81 2to3 can also refactor doctests. To enable this mode, use the :option:`-d`
82 flag. Note that *only* doctests will be refactored. This also doesn't require
83 the module to be valid Python. For example, doctest like examples in a reST
84 document could also be refactored with this option.
86 The :option:`-v` option enables output of more information on the translation
89 Since some print statements can be parsed as function calls or statements, 2to3
90 cannot always read files containing the print function. When 2to3 detects the
91 presence of the ``from __future__ import print_function`` compiler directive, it
92 modifies its internal grammar to interpert :func:`print` as a function. This
93 change can also be enabled manually with the :option:`-p` flag. Use
94 :option:`-p` to run fixers on code that already has had its print statements
103 Each step of transforming code is encapsulated in a fixer. The command ``2to3
104 -l`` lists them. As :ref:`documented above <2to3-using>`, each can be turned on
105 and off individually. They are described here in more detail.
110 Removes usage of :func:`apply`. For example ``apply(function, *args,
111 **kwargs)`` is converted to ``function(*args, **kwargs)``.
113 .. 2to3fixer:: basestring
115 Converts :class:`basestring` to :class:`str`.
117 .. 2to3fixer:: buffer
119 Converts :class:`buffer` to :class:`memoryview`. This fixer is optional
120 because the :class:`memoryview` API is similar but not exactly the same as
121 that of :class:`buffer`.
123 .. 2to3fixer:: callable
125 Converts ``callable(x)`` to ``isinstance(x, collections.Callable)``, adding
126 an import to :mod:`collections` if needed.
130 Fixes dictionary iteration methods. :meth:`dict.iteritems` is converted to
131 :meth:`dict.items`, :meth:`dict.iterkeys` to :meth:`dict.keys`, and
132 :meth:`dict.itervalues` to :meth:`dict.values`. Similarly,
133 :meth:`dict.viewitems`, :meth:`dict.viewkeys` and :meth:`dict.viewvalues`
134 are converted respectively to :meth:`dict.items`, :meth:`dict.keys` and
135 :meth:`dict.values`. It also wraps existing usages of :meth:`dict.items`,
136 :meth:`dict.keys`, and :meth:`dict.values` in a call to :class:`list`.
138 .. 2to3fixer:: except
140 Converts ``except X, T`` to ``except X as T``.
144 Converts the :keyword:`exec` statement to the :func:`exec` function.
146 .. 2to3fixer:: execfile
148 Removes usage of :func:`execfile`. The argument to :func:`execfile` is
149 wrapped in calls to :func:`open`, :func:`compile`, and :func:`exec`.
151 .. 2to3fixer:: filter
153 Wraps :func:`filter` usage in a :class:`list` call.
155 .. 2to3fixer:: funcattrs
157 Fixes function attributes that have been renamed. For example,
158 ``my_function.func_closure`` is converted to ``my_function.__closure__``.
160 .. 2to3fixer:: future
162 Removes ``from __future__ import new_feature`` statements.
164 .. 2to3fixer:: getcwdu
166 Renames :func:`os.getcwdu` to :func:`os.getcwd`.
168 .. 2to3fixer:: has_key
170 Changes ``dict.has_key(key)`` to ``key in dict``.
172 .. 2to3fixer:: idioms
174 This optional fixer performs several transformations that make Python code
175 more idiomatic. Type comparisons like ``type(x) is SomeClass`` and
176 ``type(x) == SomeClass`` are converted to ``isinstance(x, SomeClass)``.
177 ``while 1`` becomes ``while True``. This fixer also tries to make use of
178 :func:`sorted` in appropriate places. For example, this block ::
180 L = list(some_iterable)
185 L = sorted(some_iterable)
187 .. 2to3fixer:: import
189 Detects sibling imports and converts them to relative imports.
191 .. 2to3fixer:: imports
193 Handles module renames in the standard library.
195 .. 2to3fixer:: imports2
197 Handles other modules renames in the standard library. It is separate from
198 the :2to3fixer:`imports` fixer only because of technical limitations.
202 Converts ``input(prompt)`` to ``eval(input(prompt))``
204 .. 2to3fixer:: intern
206 Converts :func:`intern` to :func:`sys.intern`.
208 .. 2to3fixer:: isinstance
210 Fixes duplicate types in the second argument of :func:`isinstance`. For
211 example, ``isinstance(x, (int, int))`` is converted to ``isinstance(x,
214 .. 2to3fixer:: itertools_imports
216 Removes imports of :func:`itertools.ifilter`, :func:`itertools.izip`, and
217 :func:`itertools.imap`. Imports of :func:`itertools.ifilterfalse` are also
218 changed to :func:`itertools.filterfalse`.
220 .. 2to3fixer:: itertools
222 Changes usage of :func:`itertools.ifilter`, :func:`itertools.izip`, and
223 :func:`itertools.imap` to their built-in equivalents.
224 :func:`itertools.ifilterfalse` is changed to :func:`itertools.filterfalse`.
228 Strips the ``L`` prefix on long literals and renames :class:`long` to
233 Wraps :func:`map` in a :class:`list` call. It also changes ``map(None, x)``
234 to ``list(x)``. Using ``from future_builtins import map`` disables this
237 .. 2to3fixer:: metaclass
239 Converts the old metaclass syntax (``__metaclass__ = Meta`` in the class
240 body) to the new (``class X(metaclass=Meta)``).
242 .. 2to3fixer:: methodattrs
244 Fixes old method attribute names. For example, ``meth.im_func`` is converted
245 to ``meth.__func__``.
249 Converts the old not-equal syntax, ``<>``, to ``!=``.
253 Converts the use of iterator's :meth:`~iterator.next` methods to the
254 :func:`next` function. It also renames :meth:`next` methods to
255 :meth:`~object.__next__`.
257 .. 2to3fixer:: nonzero
259 Renames :meth:`~object.__nonzero__` to :meth:`~object.__bool__`.
261 .. 2to3fixer:: numliterals
263 Converts octal literals into the new syntax.
267 Add extra parenthesis where they are required in list comprehensions. For
268 example, ``[x for x in 1, 2]`` becomes ``[x for x in (1, 2)]``.
272 Converts the :keyword:`print` statement to the :func:`print` function.
274 .. 2to3fixer:: raises
276 Converts ``raise E, V`` to ``raise E(V)``, and ``raise E, V, T`` to ``raise
277 E(V).with_traceback(T)``. If ``E`` is a tuple, the translation will be
278 incorrect because substituting tuples for exceptions has been removed in 3.0.
280 .. 2to3fixer:: raw_input
282 Converts :func:`raw_input` to :func:`input`.
284 .. 2to3fixer:: reduce
286 Handles the move of :func:`reduce` to :func:`functools.reduce`.
288 .. 2to3fixer:: renames
290 Changes :data:`sys.maxint` to :data:`sys.maxsize`.
294 Replaces backtick repr with the :func:`repr` function.
296 .. 2to3fixer:: set_literal
298 Replaces use of the :class:`set` constructor with set literals. This fixer
301 .. 2to3fixer:: standard_error
303 Renames :exc:`StandardError` to :exc:`Exception`.
305 .. 2to3fixer:: sys_exc
307 Changes the deprecated :data:`sys.exc_value`, :data:`sys.exc_type`,
308 :data:`sys.exc_traceback` to use :func:`sys.exc_info`.
312 Fixes the API change in generator's :meth:`throw` method.
314 .. 2to3fixer:: tuple_params
316 Removes implicit tuple parameter unpacking. This fixer inserts temporary
321 Fixes code broken from the removal of some members in the :mod:`types`
324 .. 2to3fixer:: unicode
326 Renames :class:`unicode` to :class:`str`.
328 .. 2to3fixer:: urllib
330 Handles the rename of :mod:`urllib` and :mod:`urllib2` to the :mod:`urllib`
333 .. 2to3fixer:: ws_comma
335 Removes excess whitespace from comma separated items. This fixer is
338 .. 2to3fixer:: xrange
340 Renames :func:`xrange` to :func:`range` and wraps existing :func:`range`
341 calls with :class:`list`.
343 .. 2to3fixer:: xreadlines
345 Changes ``for x in file.xreadlines()`` to ``for x in file``.
349 Wraps :func:`zip` usage in a :class:`list` call. This is disabled when
350 ``from future_builtins import zip`` appears.
353 :mod:`lib2to3` - 2to3's library
354 -------------------------------
357 :synopsis: the 2to3 library
358 .. moduleauthor:: Guido van Rossum
359 .. moduleauthor:: Collin Winter
360 .. moduleauthor:: Benjamin Peterson <benjamin@python.org>
365 The :mod:`lib2to3` API should be considered unstable and may change
366 drastically in the future.
368 .. XXX What is the public interface anyway?