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2to3 - Automated Python 2 to 3 code translation
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===============================================
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.. sectionauthor:: Benjamin Peterson
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2to3 is a Python program that reads Python 2.x source code and applies a series
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of *fixers* to transform it into valid Python 3.x code. The standard library
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contains a rich set of fixers that will handle almost all code. 2to3 supporting
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library :mod:`lib2to3` is, however, a flexible and generic library, so it is
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possible to write your own fixers for 2to3. :mod:`lib2to3` could also be
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adapted to custom applications in which Python code needs to be edited
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2to3 will usually be installed with the Python interpreter as a script. It is
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also located in the :file:`Tools/scripts` directory of the Python root.
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2to3's basic arguments are a list of files or directories to transform. The
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directories are to recursively traversed for Python sources.
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Here is a sample Python 2.x source file, :file:`example.py`::
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print "Hello, {0}!".format(name)
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print "What's your name?"
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It can be converted to Python 3.x code via 2to3 on the command line::
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A diff against the original source file is printed. 2to3 can also write the
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needed modifications right back to the source file. (Of course, a backup of the
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original is also be made.) Writing the changes back is enabled with the
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After transformation, :file:`example.py` looks like this::
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print("Hello, {0}!".format(name))
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print("What's your name?")
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Comments and and exact indentation are preserved throughout the translation
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By default, 2to3 runs a set of predefined fixers. The :option:`-l` flag
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lists all avaible fixers. An explicit set of fixers to run can be given by use
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of the :option:`-f` flag. The following example runs only the ``imports`` and
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$ 2to3 -f imports -f has_key example.py
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Some fixers are *explicit*, meaning they aren't run be default and must be
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listed on the command line to be run. Here, in addition to the default fixers,
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the ``idioms`` fixer is run::
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$ 2to3 -f all -f idioms example.py
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Notice how passing ``all`` enables all default fixers.
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Sometimes 2to3 will find will find a place in your source code that needs to be
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changed, but 2to3 cannot fix automatically. In this case, 2to3 will print a
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warning beneath the diff for a file. You should address the warning in order to
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have compliant 3.x code.
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2to3 can also refactor doctests. To enable this mode, use the :option:`-d`
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flag. Note that *only* doctests will be refactored.
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The :option:`-v` option enables the output of more information on the
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When the :option:`-p` is passed, 2to3 treats ``print`` as a function instead of
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a statement. This is useful when ``from __future__ import print_function`` is
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being used. If this option is not given, the print fixer will surround print
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calls in an extra set of parentheses because it cannot differentiate between the
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and print statement with parentheses (such as ``print ("a" + "b" + "c")``) and a
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:mod:`lib2to3` - 2to3's library
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-------------------------------
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:synopsis: the 2to3 library
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.. moduleauthor:: Guido van Rossum
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.. moduleauthor:: Collin Winter
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.. XXX What is the public interface anyway?
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Doc/library/2to3.rst
