474 lines
15 KiB
ReStructuredText
474 lines
15 KiB
ReStructuredText
.. _2to3-reference:
|
|
|
|
2to3 - Automated Python 2 to 3 code translation
|
|
===============================================
|
|
|
|
.. sectionauthor:: Benjamin Peterson <benjamin@python.org>
|
|
|
|
2to3 is a Python program that reads Python 2.x source code and applies a series
|
|
of *fixers* to transform it into valid Python 3.x code. The standard library
|
|
contains a rich set of fixers that will handle almost all code. 2to3 supporting
|
|
library :mod:`lib2to3` is, however, a flexible and generic library, so it is
|
|
possible to write your own fixers for 2to3. :mod:`lib2to3` could also be
|
|
adapted to custom applications in which Python code needs to be edited
|
|
automatically.
|
|
|
|
|
|
.. _2to3-using:
|
|
|
|
Using 2to3
|
|
----------
|
|
|
|
2to3 will usually be installed with the Python interpreter as a script. It is
|
|
also located in the :file:`Tools/scripts` directory of the Python root.
|
|
|
|
2to3's basic arguments are a list of files or directories to transform. The
|
|
directories are recursively traversed for Python sources.
|
|
|
|
Here is a sample Python 2.x source file, :file:`example.py`::
|
|
|
|
def greet(name):
|
|
print "Hello, {0}!".format(name)
|
|
print "What's your name?"
|
|
name = raw_input()
|
|
greet(name)
|
|
|
|
It can be converted to Python 3.x code via 2to3 on the command line:
|
|
|
|
.. code-block:: shell-session
|
|
|
|
$ 2to3 example.py
|
|
|
|
A diff against the original source file is printed. 2to3 can also write the
|
|
needed modifications right back to the source file. (A backup of the original
|
|
file is made unless :option:`!-n` is also given.) Writing the changes back is
|
|
enabled with the :option:`!-w` flag:
|
|
|
|
.. code-block:: shell-session
|
|
|
|
$ 2to3 -w example.py
|
|
|
|
After transformation, :file:`example.py` looks like this::
|
|
|
|
def greet(name):
|
|
print("Hello, {0}!".format(name))
|
|
print("What's your name?")
|
|
name = input()
|
|
greet(name)
|
|
|
|
Comments and exact indentation are preserved throughout the translation process.
|
|
|
|
By default, 2to3 runs a set of :ref:`predefined fixers <2to3-fixers>`. The
|
|
:option:`!-l` flag lists all available fixers. An explicit set of fixers to run
|
|
can be given with :option:`!-f`. Likewise the :option:`!-x` explicitly disables a
|
|
fixer. The following example runs only the ``imports`` and ``has_key`` fixers:
|
|
|
|
.. code-block:: shell-session
|
|
|
|
$ 2to3 -f imports -f has_key example.py
|
|
|
|
This command runs every fixer except the ``apply`` fixer:
|
|
|
|
.. code-block:: shell-session
|
|
|
|
$ 2to3 -x apply example.py
|
|
|
|
Some fixers are *explicit*, meaning they aren't run by default and must be
|
|
listed on the command line to be run. Here, in addition to the default fixers,
|
|
the ``idioms`` fixer is run:
|
|
|
|
.. code-block:: shell-session
|
|
|
|
$ 2to3 -f all -f idioms example.py
|
|
|
|
Notice how passing ``all`` enables all default fixers.
|
|
|
|
Sometimes 2to3 will find a place in your source code that needs to be changed,
|
|
but 2to3 cannot fix automatically. In this case, 2to3 will print a warning
|
|
beneath the diff for a file. You should address the warning in order to have
|
|
compliant 3.x code.
|
|
|
|
2to3 can also refactor doctests. To enable this mode, use the :option:`!-d`
|
|
flag. Note that *only* doctests will be refactored. This also doesn't require
|
|
the module to be valid Python. For example, doctest like examples in a reST
|
|
document could also be refactored with this option.
|
|
|
|
The :option:`!-v` option enables output of more information on the translation
|
|
process.
|
|
|
|
Since some print statements can be parsed as function calls or statements, 2to3
|
|
cannot always read files containing the print function. When 2to3 detects the
|
|
presence of the ``from __future__ import print_function`` compiler directive, it
|
|
modifies its internal grammar to interpret :func:`print` as a function. This
|
|
change can also be enabled manually with the :option:`!-p` flag. Use
|
|
:option:`!-p` to run fixers on code that already has had its print statements
|
|
converted.
|
|
|
|
The :option:`!-o` or :option:`!--output-dir` option allows specification of an
|
|
alternate directory for processed output files to be written to. The
|
|
:option:`!-n` flag is required when using this as backup files do not make sense
|
|
when not overwriting the input files.
|
|
|
|
.. versionadded:: 3.2.3
|
|
The :option:`!-o` option was added.
|
|
|
|
The :option:`!-W` or :option:`!--write-unchanged-files` flag tells 2to3 to always
|
|
write output files even if no changes were required to the file. This is most
|
|
useful with :option:`!-o` so that an entire Python source tree is copied with
|
|
translation from one directory to another.
|
|
This option implies the :option:`!-w` flag as it would not make sense otherwise.
|
|
|
|
.. versionadded:: 3.2.3
|
|
The :option:`!-W` flag was added.
|
|
|
|
The :option:`!--add-suffix` option specifies a string to append to all output
|
|
filenames. The :option:`!-n` flag is required when specifying this as backups
|
|
are not necessary when writing to different filenames. Example:
|
|
|
|
.. code-block:: shell-session
|
|
|
|
$ 2to3 -n -W --add-suffix=3 example.py
|
|
|
|
Will cause a converted file named ``example.py3`` to be written.
|
|
|
|
.. versionadded:: 3.2.3
|
|
The :option:`!--add-suffix` option was added.
|
|
|
|
To translate an entire project from one directory tree to another use:
|
|
|
|
.. code-block:: shell-session
|
|
|
|
$ 2to3 --output-dir=python3-version/mycode -W -n python2-version/mycode
|
|
|
|
|
|
.. _2to3-fixers:
|
|
|
|
Fixers
|
|
------
|
|
|
|
Each step of transforming code is encapsulated in a fixer. The command ``2to3
|
|
-l`` lists them. As :ref:`documented above <2to3-using>`, each can be turned on
|
|
and off individually. They are described here in more detail.
|
|
|
|
|
|
.. 2to3fixer:: apply
|
|
|
|
Removes usage of :func:`apply`. For example ``apply(function, *args,
|
|
**kwargs)`` is converted to ``function(*args, **kwargs)``.
|
|
|
|
.. 2to3fixer:: asserts
|
|
|
|
Replaces deprecated :mod:`unittest` method names with the correct ones.
|
|
|
|
================================ ==========================================
|
|
From To
|
|
================================ ==========================================
|
|
``failUnlessEqual(a, b)`` :meth:`assertEqual(a, b)
|
|
<unittest.TestCase.assertEqual>`
|
|
``assertEquals(a, b)`` :meth:`assertEqual(a, b)
|
|
<unittest.TestCase.assertEqual>`
|
|
``failIfEqual(a, b)`` :meth:`assertNotEqual(a, b)
|
|
<unittest.TestCase.assertNotEqual>`
|
|
``assertNotEquals(a, b)`` :meth:`assertNotEqual(a, b)
|
|
<unittest.TestCase.assertNotEqual>`
|
|
``failUnless(a)`` :meth:`assertTrue(a)
|
|
<unittest.TestCase.assertTrue>`
|
|
``assert_(a)`` :meth:`assertTrue(a)
|
|
<unittest.TestCase.assertTrue>`
|
|
``failIf(a)`` :meth:`assertFalse(a)
|
|
<unittest.TestCase.assertFalse>`
|
|
``failUnlessRaises(exc, cal)`` :meth:`assertRaises(exc, cal)
|
|
<unittest.TestCase.assertRaises>`
|
|
``failUnlessAlmostEqual(a, b)`` :meth:`assertAlmostEqual(a, b)
|
|
<unittest.TestCase.assertAlmostEqual>`
|
|
``assertAlmostEquals(a, b)`` :meth:`assertAlmostEqual(a, b)
|
|
<unittest.TestCase.assertAlmostEqual>`
|
|
``failIfAlmostEqual(a, b)`` :meth:`assertNotAlmostEqual(a, b)
|
|
<unittest.TestCase.assertNotAlmostEqual>`
|
|
``assertNotAlmostEquals(a, b)`` :meth:`assertNotAlmostEqual(a, b)
|
|
<unittest.TestCase.assertNotAlmostEqual>`
|
|
================================ ==========================================
|
|
|
|
.. 2to3fixer:: basestring
|
|
|
|
Converts :class:`basestring` to :class:`str`.
|
|
|
|
.. 2to3fixer:: buffer
|
|
|
|
Converts :class:`buffer` to :class:`memoryview`. This fixer is optional
|
|
because the :class:`memoryview` API is similar but not exactly the same as
|
|
that of :class:`buffer`.
|
|
|
|
.. 2to3fixer:: dict
|
|
|
|
Fixes dictionary iteration methods. :meth:`dict.iteritems` is converted to
|
|
:meth:`dict.items`, :meth:`dict.iterkeys` to :meth:`dict.keys`, and
|
|
:meth:`dict.itervalues` to :meth:`dict.values`. Similarly,
|
|
:meth:`dict.viewitems`, :meth:`dict.viewkeys` and :meth:`dict.viewvalues` are
|
|
converted respectively to :meth:`dict.items`, :meth:`dict.keys` and
|
|
:meth:`dict.values`. It also wraps existing usages of :meth:`dict.items`,
|
|
:meth:`dict.keys`, and :meth:`dict.values` in a call to :class:`list`.
|
|
|
|
.. 2to3fixer:: except
|
|
|
|
Converts ``except X, T`` to ``except X as T``.
|
|
|
|
.. 2to3fixer:: exec
|
|
|
|
Converts the ``exec`` statement to the :func:`exec` function.
|
|
|
|
.. 2to3fixer:: execfile
|
|
|
|
Removes usage of :func:`execfile`. The argument to :func:`execfile` is
|
|
wrapped in calls to :func:`open`, :func:`compile`, and :func:`exec`.
|
|
|
|
.. 2to3fixer:: exitfunc
|
|
|
|
Changes assignment of :attr:`sys.exitfunc` to use of the :mod:`atexit`
|
|
module.
|
|
|
|
.. 2to3fixer:: filter
|
|
|
|
Wraps :func:`filter` usage in a :class:`list` call.
|
|
|
|
.. 2to3fixer:: funcattrs
|
|
|
|
Fixes function attributes that have been renamed. For example,
|
|
``my_function.func_closure`` is converted to ``my_function.__closure__``.
|
|
|
|
.. 2to3fixer:: future
|
|
|
|
Removes ``from __future__ import new_feature`` statements.
|
|
|
|
.. 2to3fixer:: getcwdu
|
|
|
|
Renames :func:`os.getcwdu` to :func:`os.getcwd`.
|
|
|
|
.. 2to3fixer:: has_key
|
|
|
|
Changes ``dict.has_key(key)`` to ``key in dict``.
|
|
|
|
.. 2to3fixer:: idioms
|
|
|
|
This optional fixer performs several transformations that make Python code
|
|
more idiomatic. Type comparisons like ``type(x) is SomeClass`` and
|
|
``type(x) == SomeClass`` are converted to ``isinstance(x, SomeClass)``.
|
|
``while 1`` becomes ``while True``. This fixer also tries to make use of
|
|
:func:`sorted` in appropriate places. For example, this block ::
|
|
|
|
L = list(some_iterable)
|
|
L.sort()
|
|
|
|
is changed to ::
|
|
|
|
L = sorted(some_iterable)
|
|
|
|
.. 2to3fixer:: import
|
|
|
|
Detects sibling imports and converts them to relative imports.
|
|
|
|
.. 2to3fixer:: imports
|
|
|
|
Handles module renames in the standard library.
|
|
|
|
.. 2to3fixer:: imports2
|
|
|
|
Handles other modules renames in the standard library. It is separate from
|
|
the :2to3fixer:`imports` fixer only because of technical limitations.
|
|
|
|
.. 2to3fixer:: input
|
|
|
|
Converts ``input(prompt)`` to ``eval(input(prompt))``.
|
|
|
|
.. 2to3fixer:: intern
|
|
|
|
Converts :func:`intern` to :func:`sys.intern`.
|
|
|
|
.. 2to3fixer:: isinstance
|
|
|
|
Fixes duplicate types in the second argument of :func:`isinstance`. For
|
|
example, ``isinstance(x, (int, int))`` is converted to ``isinstance(x,
|
|
(int))``.
|
|
|
|
.. 2to3fixer:: itertools_imports
|
|
|
|
Removes imports of :func:`itertools.ifilter`, :func:`itertools.izip`, and
|
|
:func:`itertools.imap`. Imports of :func:`itertools.ifilterfalse` are also
|
|
changed to :func:`itertools.filterfalse`.
|
|
|
|
.. 2to3fixer:: itertools
|
|
|
|
Changes usage of :func:`itertools.ifilter`, :func:`itertools.izip`, and
|
|
:func:`itertools.imap` to their built-in equivalents.
|
|
:func:`itertools.ifilterfalse` is changed to :func:`itertools.filterfalse`.
|
|
|
|
.. 2to3fixer:: long
|
|
|
|
Renames :class:`long` to :class:`int`.
|
|
|
|
.. 2to3fixer:: map
|
|
|
|
Wraps :func:`map` in a :class:`list` call. It also changes ``map(None, x)``
|
|
to ``list(x)``. Using ``from future_builtins import map`` disables this
|
|
fixer.
|
|
|
|
.. 2to3fixer:: metaclass
|
|
|
|
Converts the old metaclass syntax (``__metaclass__ = Meta`` in the class
|
|
body) to the new (``class X(metaclass=Meta)``).
|
|
|
|
.. 2to3fixer:: methodattrs
|
|
|
|
Fixes old method attribute names. For example, ``meth.im_func`` is converted
|
|
to ``meth.__func__``.
|
|
|
|
.. 2to3fixer:: ne
|
|
|
|
Converts the old not-equal syntax, ``<>``, to ``!=``.
|
|
|
|
.. 2to3fixer:: next
|
|
|
|
Converts the use of iterator's :meth:`~iterator.next` methods to the
|
|
:func:`next` function. It also renames :meth:`next` methods to
|
|
:meth:`~iterator.__next__`.
|
|
|
|
.. 2to3fixer:: nonzero
|
|
|
|
Renames :meth:`__nonzero__` to :meth:`~object.__bool__`.
|
|
|
|
.. 2to3fixer:: numliterals
|
|
|
|
Converts octal literals into the new syntax.
|
|
|
|
.. 2to3fixer:: operator
|
|
|
|
Converts calls to various functions in the :mod:`operator` module to other,
|
|
but equivalent, function calls. When needed, the appropriate ``import``
|
|
statements are added, e.g. ``import collections``. The following mapping
|
|
are made:
|
|
|
|
================================== ==========================================
|
|
From To
|
|
================================== ==========================================
|
|
``operator.isCallable(obj)`` ``hasattr(obj, '__call__')``
|
|
``operator.sequenceIncludes(obj)`` ``operator.contains(obj)``
|
|
``operator.isSequenceType(obj)`` ``isinstance(obj, collections.Sequence)``
|
|
``operator.isMappingType(obj)`` ``isinstance(obj, collections.Mapping)``
|
|
``operator.isNumberType(obj)`` ``isinstance(obj, numbers.Number)``
|
|
``operator.repeat(obj, n)`` ``operator.mul(obj, n)``
|
|
``operator.irepeat(obj, n)`` ``operator.imul(obj, n)``
|
|
================================== ==========================================
|
|
|
|
.. 2to3fixer:: paren
|
|
|
|
Add extra parenthesis where they are required in list comprehensions. For
|
|
example, ``[x for x in 1, 2]`` becomes ``[x for x in (1, 2)]``.
|
|
|
|
.. 2to3fixer:: print
|
|
|
|
Converts the ``print`` statement to the :func:`print` function.
|
|
|
|
.. 2to3fixer:: raise
|
|
|
|
Converts ``raise E, V`` to ``raise E(V)``, and ``raise E, V, T`` to ``raise
|
|
E(V).with_traceback(T)``. If ``E`` is a tuple, the translation will be
|
|
incorrect because substituting tuples for exceptions has been removed in 3.0.
|
|
|
|
.. 2to3fixer:: raw_input
|
|
|
|
Converts :func:`raw_input` to :func:`input`.
|
|
|
|
.. 2to3fixer:: reduce
|
|
|
|
Handles the move of :func:`reduce` to :func:`functools.reduce`.
|
|
|
|
.. 2to3fixer:: reload
|
|
|
|
Converts :func:`reload` to :func:`imp.reload`.
|
|
|
|
.. 2to3fixer:: renames
|
|
|
|
Changes :data:`sys.maxint` to :data:`sys.maxsize`.
|
|
|
|
.. 2to3fixer:: repr
|
|
|
|
Replaces backtick repr with the :func:`repr` function.
|
|
|
|
.. 2to3fixer:: set_literal
|
|
|
|
Replaces use of the :class:`set` constructor with set literals. This fixer
|
|
is optional.
|
|
|
|
.. 2to3fixer:: standarderror
|
|
|
|
Renames :exc:`StandardError` to :exc:`Exception`.
|
|
|
|
.. 2to3fixer:: sys_exc
|
|
|
|
Changes the deprecated :data:`sys.exc_value`, :data:`sys.exc_type`,
|
|
:data:`sys.exc_traceback` to use :func:`sys.exc_info`.
|
|
|
|
.. 2to3fixer:: throw
|
|
|
|
Fixes the API change in generator's :meth:`throw` method.
|
|
|
|
.. 2to3fixer:: tuple_params
|
|
|
|
Removes implicit tuple parameter unpacking. This fixer inserts temporary
|
|
variables.
|
|
|
|
.. 2to3fixer:: types
|
|
|
|
Fixes code broken from the removal of some members in the :mod:`types`
|
|
module.
|
|
|
|
.. 2to3fixer:: unicode
|
|
|
|
Renames :class:`unicode` to :class:`str`.
|
|
|
|
.. 2to3fixer:: urllib
|
|
|
|
Handles the rename of :mod:`urllib` and :mod:`urllib2` to the :mod:`urllib`
|
|
package.
|
|
|
|
.. 2to3fixer:: ws_comma
|
|
|
|
Removes excess whitespace from comma separated items. This fixer is
|
|
optional.
|
|
|
|
.. 2to3fixer:: xrange
|
|
|
|
Renames :func:`xrange` to :func:`range` and wraps existing :func:`range`
|
|
calls with :class:`list`.
|
|
|
|
.. 2to3fixer:: xreadlines
|
|
|
|
Changes ``for x in file.xreadlines()`` to ``for x in file``.
|
|
|
|
.. 2to3fixer:: zip
|
|
|
|
Wraps :func:`zip` usage in a :class:`list` call. This is disabled when
|
|
``from future_builtins import zip`` appears.
|
|
|
|
|
|
:mod:`lib2to3` - 2to3's library
|
|
-------------------------------
|
|
|
|
.. module:: lib2to3
|
|
:synopsis: the 2to3 library
|
|
|
|
.. moduleauthor:: Guido van Rossum
|
|
.. moduleauthor:: Collin Winter
|
|
.. moduleauthor:: Benjamin Peterson <benjamin@python.org>
|
|
|
|
**Source code:** :source:`Lib/lib2to3/`
|
|
|
|
--------------
|
|
|
|
.. note::
|
|
|
|
The :mod:`lib2to3` API should be considered unstable and may change
|
|
drastically in the future.
|
|
|
|
.. XXX What is the public interface anyway?
|