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Doc/library/tokenize.rst

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+
+: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 generator:
+
+
+.. function:: generate_tokens(readline)
+
+   The :func:`generate_tokens` generator requires one argment, *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 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)
+