1 

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

     3 ===============================================

     4 

     5 .. module:: tokenize

     6    :synopsis: Lexical scanner for Python source code.

     7 .. moduleauthor:: Ka Ping Yee

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

     9 

    10 

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

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

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

    14 for on-screen displays.

    15 

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

    17 

    18 .. function:: generate_tokens(readline)

    19 

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

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

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

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

    24    of input as a string.

    25 

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

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

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

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

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

    31    the *logical* line; continuation lines are included.

    32 

    33    .. versionadded:: 2.2

    34 

    35 An older entry point is retained for backward compatibility:

    36 

    37 

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

    39 

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

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

    42 

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

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

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

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

    47    signals completion by raising :exc:`StopIteration`.

    48 

    49    .. versionchanged:: 2.5

    50       Added :exc:`StopIteration` support.

    51 

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

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

    54    generated by :func:`generate_tokens`.

    55 

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

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

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

    59 

    60 

    61 .. data:: COMMENT

    62 

    63    Token value used to indicate a comment.

    64 

    65 

    66 .. data:: NL

    67 

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

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

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

    71 

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

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

    74 back the modified script.

    75 

    76 

    77 .. function:: untokenize(iterable)

    78 

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

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

    81    additional sequence elements are ignored.

    82 

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

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

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

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

    87    change.

    88 

    89    .. versionadded:: 2.5

    90 

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

    92 objects::

    93 

    94    def decistmt(s):

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

    96 

    97        >>> from decimal import Decimal

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

    99        >>> decistmt(s)

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

   101 

   102        >>> exec(s)

   103        -3.21716034272e-007

   104        >>> exec(decistmt(s))

   105        -3.217160342717258261933904529E-7

   106 

   107        """

   108        result = []

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

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

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

   112                result.extend([

   113                    (NAME, 'Decimal'),

   114                    (OP, '('),

   115                    (STRING, repr(tokval)),

   116                    (OP, ')')

   117                ])

   118            else:

   119                result.append((toknum, tokval))

   120        return untokenize(result)

   121