: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:`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`.
.. warning::
Note that the functions in this module are only designed to parse
syntactically valid Python code (code that does not raise when parsed
using :func:`ast.parse`). The behavior of the functions in this module is
**undefined** when providing invalid Python code and it can change at any
point.
Tokenizing Input
----------------
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
.. _tokenize-cli:
Command-Line Usage
------------------
.. versionadded:: 3.3
The :mod:`tokenize` module can be executed as a script from the command line.
It is as simple as:
.. code-block:: sh
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.
Examples
------------------
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)
.. code-block:: shell-session
$ 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:
.. code-block:: shell-session
$ 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 ''
Example of tokenizing a file programmatically, reading unicode
strings instead of bytes with :func:`generate_tokens`::
import tokenize
with tokenize.open('hello.py') as f:
tokens = tokenize.generate_tokens(f.readline)
for token in tokens:
print(token)
Or reading bytes directly with :func:`.tokenize`::
import tokenize
with open('hello.py', 'rb') as f:
tokens = tokenize.tokenize(f.readline)
for token in tokens:
print(token)