:mod:`tokenize` --- Tokenizer for Python source

===============================================

.. module:: tokenize

   :synopsis: Lexical scanner for Python source code.

.. moduleauthor:: Ka Ping Yee

.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>

The :mod:`tokenize` module provides a lexical scanner for Python source code,

implemented in Python.  The scanner in this module returns comments as tokens as

well, making it useful for implementing "pretty-printers," including colorizers

for on-screen displays.

The primary entry point is a :term:`generator`:

.. function:: generate_tokens(readline)

   The :func:`generate_tokens` generator requires one argument, *readline*,

   which must be a callable object which provides the same interface as the

   :meth:`readline` method of built-in file objects (see section

   :ref:`bltin-file-objects`).  Each call to the function should return one line

   of input as a string.

   The generator produces 5-tuples with these members: the token type; the token

   string; a 2-tuple ``(srow, scol)`` of ints specifying the row and column

   where the token begins in the source; a 2-tuple ``(erow, ecol)`` of ints

   specifying the row and column where the token ends in the source; and the

   line on which the token was found.  The line passed (the last tuple item) is

   the *logical* line; continuation lines are included.

   .. versionadded:: 2.2

An older entry point is retained for backward compatibility:

.. function:: tokenize(readline[, tokeneater])

   The :func:`tokenize` function accepts two parameters: one representing the input

   stream, and one providing an output mechanism for :func:`tokenize`.

   The first parameter, *readline*, must be a callable object which provides the

   same interface as the :meth:`readline` method of built-in file objects (see

   section :ref:`bltin-file-objects`).  Each call to the function should return one

   line of input as a string. Alternately, *readline* may be a callable object that

   signals completion by raising :exc:`StopIteration`.

   .. versionchanged:: 2.5

      Added :exc:`StopIteration` support.

   The second parameter, *tokeneater*, must also be a callable object.  It is

   called once for each token, with five arguments, corresponding to the tuples

   generated by :func:`generate_tokens`.

All constants from the :mod:`token` module are also exported from

:mod:`tokenize`, as are two additional token type values that might be passed to

the *tokeneater* function by :func:`tokenize`:

.. data:: COMMENT

   Token value used to indicate a comment.

.. data:: NL

   Token value used to indicate a non-terminating newline.  The NEWLINE token

   indicates the end of a logical line of Python code; NL tokens are generated when

   a logical line of code is continued over multiple physical lines.

Another function is provided to reverse the tokenization process. This is useful

for creating tools that tokenize a script, modify the token stream, and write

back the modified script.

.. function:: untokenize(iterable)

   Converts tokens back into Python source code.  The *iterable* must return

   sequences with at least two elements, the token type and the token string.  Any

   additional sequence elements are ignored.

   The reconstructed script is returned as a single string.  The result is

   guaranteed to tokenize back to match the input so that the conversion is

   lossless and round-trips are assured.  The guarantee applies only to the token

   type and token string as the spacing between tokens (column positions) may

   change.

   .. versionadded:: 2.5

Example of a script re-writer that transforms float literals into Decimal

objects::

   def decistmt(s):

       """Substitute Decimals for floats in a string of statements.

       >>> from decimal import Decimal

       >>> s = 'print +21.3e-5*-.1234/81.7'

       >>> decistmt(s)

       "print +Decimal ('21.3e-5')*-Decimal ('.1234')/Decimal ('81.7')"

       >>> exec(s)

       -3.21716034272e-007

       >>> exec(decistmt(s))

       -3.217160342717258261933904529E-7

       """

       result = []

       g = generate_tokens(StringIO(s).readline)   # tokenize the string

       for toknum, tokval, _, _, _  in g:

           if toknum == NUMBER and '.' in tokval:  # replace NUMBER tokens

               result.extend([

                   (NAME, 'Decimal'),

                   (OP, '('),

                   (STRING, repr(tokval)),

                   (OP, ')')

               ])

           else:

               result.append((toknum, tokval))

       return untokenize(result)