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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>
**Source code:** :source:`Lib/tokenize.py`
--------------
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.
To simplify token stream handling, all :ref:`operators` and :ref:`delimiters`
tokens are returned using the generic :data:`token.OP` token type. The exact
type can be determined by checking the second field (containing the actual
token string matched) of the tuple returned from
:func:`tokenize.generate_tokens` for the character sequence that identifies a
specific operator token.
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:`~file.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`.
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:`~file.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
.. exception:: TokenError
Raised when either a docstring or expression that may be split over several
lines is not completed anywhere in the file, for example::
"""Beginning of
docstring
or::
[1,
2,
3
Note that unclosed single-quoted strings do not cause an error to be
raised. They are tokenized as ``ERRORTOKEN``, followed by the tokenization of
their contents.
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)