cpython/Doc/library/2to3.rst

.. _2to3-reference:

2to3 - Automated Python 2 to 3 code translation
===============================================

.. sectionauthor:: Benjamin Peterson

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.  It is, however,
possible to write your own fixers.


Using 2to3
----------

2to3 can be run with a list of files to transform or a directory to recursively
traverse looking for files with the ``.py`` extension.

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::

   $ 2to3 example.py

A diff against the original source file will be printed.  2to3 can also write
the needed modifications right back to the source file.  (A backup of the
original file will also be made.)  This is done with the :option:`-w` flag::

   $ 2to3 -w example.py

:file:`example.py` will now look like this::

   def greet(name):
       print("Hello, {0}!".format(name))
   print("What's your name?")
   name = input()
   greet(name)

Comments and and exact indentation will be preserved throughout the translation
process.

By default, 2to3 will run a set of predefined fixers.  The :option:`-l` flag
lists all avaible fixers.  An explicit set of fixers to run can be given by use
of the :option:`-f` flag.  The following example runs only the ``imports`` and
``has_key`` fixers::

   $ 2to3 -f imports -f has_key example.py

Some fixers are *explicit*, meaning they aren't run be default and must be
listed on the command line.  Here, in addition to the default fixers, the
``idioms`` fixer is run::

   $ 2to3 -f all -f idioms example.py

Notice how ``all`` enables all default fixers.

Sometimes 2to3 will find 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.


:mod:`lib2to3` - 2to3's library
-------------------------------

.. module:: lib2to3
   :synopsis: the 2to3 library
.. moduleauthor:: Guido van Rossum
.. moduleauthor:: Collin Winter

.. XXX What is the public interface anyway?