.. 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:`operator <operators>` and
:ref:`delimiter <delimiters>` tokens and :data:`Ellipsis` are returned using
the generic :data:`~token.OP` token type. The exact
type can be determined by checking the exact_type property on the
:term:`named tuple` returned from :func:`tokenize.tokenize`.
The primary entry point is a :term:`generator`:
.. function:: tokenize(readline) The :func:`.tokenize` generator requires one argument, *readline*, which must be a callable object which provides the same interface as the :meth:`io.IOBase.readline` method of file objects. Each call to the function should return one line of input as bytes. 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 *physical* line. The 5 tuple is returned as a :term:`named tuple` with the field names: ``type string start end line``. The returned :term:`named tuple` has an additional property named ``exact_type`` that contains the exact operator type for :data:`~token.OP` tokens. For all other token types ``exact_type`` equals the named tuple ``type`` field. .. versionchanged:: 3.1 Added support for named tuples. .. versionchanged:: 3.3 Added support for ``exact_type``. :func:`.tokenize` determines the source encoding of the file by looking for a UTF-8 BOM or encoding cookie, according to :pep:`263`.
.. function:: generate_tokens(readline) Tokenize a source reading unicode strings instead of bytes. Like :func:`.tokenize`, the *readline* argument is a callable returning a single line of input. However, :func:`generate_tokens` expects *readline* to return a str object rather than bytes. The result is an iterator yielding named tuples, exactly like :func:`.tokenize`. It does not yield an :data:`~token.ENCODING` token.
All constants from the :mod:`token` module are also exported from :mod:`tokenize`.
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. It returns bytes, encoded using the :data:`~token.ENCODING` token, which is the first token sequence output by :func:`.tokenize`. If there is no encoding token in the input, it returns a str instead.
:func:`.tokenize` needs to detect the encoding of source files it tokenizes. The function it uses to do this is available:
.. function:: detect_encoding(readline) The :func:`detect_encoding` function is used to detect the encoding that should be used to decode a Python source file. It requires one argument, readline, in the same way as the :func:`.tokenize` generator. It will call readline a maximum of twice, and return the encoding used (as a string) and a list of any lines (not decoded from bytes) it has read in. It detects the encoding from the presence of a UTF-8 BOM or an encoding cookie as specified in :pep:`263`. If both a BOM and a cookie are present, but disagree, a :exc:`SyntaxError` will be raised. Note that if the BOM is found, ``'utf-8-sig'`` will be returned as an encoding. If no encoding is specified, then the default of ``'utf-8'`` will be returned. Use :func:`.open` to open Python source files: it uses :func:`detect_encoding` to detect the file encoding.
.. function:: open(filename) Open a file in read only mode using the encoding detected by :func:`detect_encoding`. .. versionadded:: 3.2
.. 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 :data:`~token.ERRORTOKEN`, followed by the tokenization of their contents.
.. versionadded:: 3.3
The :mod:`tokenize` module can be executed as a script from the command line. It is as simple as:
python -m tokenize [-e] [filename.py]
The following options are accepted:
.. program:: tokenize
.. cmdoption:: -h, --help show this help message and exit
.. cmdoption:: -e, --exact display token names using the exact type
If :file:`filename.py` is specified its contents are tokenized to stdout. Otherwise, tokenization is performed on stdin.
Example of a script rewriter that transforms float literals into Decimal objects:
from tokenize import tokenize, untokenize, NUMBER, STRING, NAME, OP
from io import BytesIO
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'))"
The format of the exponent is inherited from the platform C library.
Known cases are "e-007" (Windows) and "e-07" (not Windows). Since
we're only showing 12 digits, and the 13th isn't close to 5, the
rest of the output should be platform-independent.
>>> exec(s) #doctest: +ELLIPSIS
-3.21716034272e-0...7
Output from calculations with Decimal should be identical across all
platforms.
>>> exec(decistmt(s))
-3.217160342717258261933904529E-7
"""
result = []
g = tokenize(BytesIO(s.encode('utf-8')).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).decode('utf-8')
Example of tokenizing from the command line. The script:
def say_hello():
print("Hello, World!")
say_hello()
will be tokenized to the following output where the first column is the range of the line/column coordinates where the token is found, the second column is the name of the token, and the final column is the value of the token (if any)
$ python -m tokenize hello.py
0,0-0,0: ENCODING 'utf-8'
1,0-1,3: NAME 'def'
1,4-1,13: NAME 'say_hello'
1,13-1,14: OP '('
1,14-1,15: OP ')'
1,15-1,16: OP ':'
1,16-1,17: NEWLINE '\n'
2,0-2,4: INDENT ' '
2,4-2,9: NAME 'print'
2,9-2,10: OP '('
2,10-2,25: STRING '"Hello, World!"'
2,25-2,26: OP ')'
2,26-2,27: NEWLINE '\n'
3,0-3,1: NL '\n'
4,0-4,0: DEDENT ''
4,0-4,9: NAME 'say_hello'
4,9-4,10: OP '('
4,10-4,11: OP ')'
4,11-4,12: NEWLINE '\n'
5,0-5,0: ENDMARKER ''
The exact token type names can be displayed using the :option:`-e` option:
$ python -m tokenize -e hello.py
0,0-0,0: ENCODING 'utf-8'
1,0-1,3: NAME 'def'
1,4-1,13: NAME 'say_hello'
1,13-1,14: LPAR '('
1,14-1,15: RPAR ')'
1,15-1,16: COLON ':'
1,16-1,17: NEWLINE '\n'
2,0-2,4: INDENT ' '
2,4-2,9: NAME 'print'
2,9-2,10: LPAR '('
2,10-2,25: STRING '"Hello, World!"'
2,25-2,26: RPAR ')'
2,26-2,27: NEWLINE '\n'
3,0-3,1: NL '\n'
4,0-4,0: DEDENT ''
4,0-4,9: NAME 'say_hello'
4,9-4,10: LPAR '('
4,10-4,11: RPAR ')'
4,11-4,12: NEWLINE '\n'
5,0-5,0: ENDMARKER ''
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