Python 3.6.5 Documentation >  "tokenize" — Tokenizer for Python source

"tokenize" — Tokenizer for Python source
****************************************

**Source code:** Lib/tokenize.py

======================================================================

The "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 operator and delimiter tokens
and "Ellipsis" are returned using the generic "OP" token type. The
exact type can be determined by checking the "exact_type" property on
the *named tuple* returned from "tokenize.tokenize()".

Tokenizing Input
================

The primary entry point is a *generator*:

tokenize.tokenize(readline)

The "tokenize()" generator requires one argument, *readline*, which
must be a callable object which provides the same interface as the
"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 *logical* line;
continuation lines are included. The 5 tuple is returned as a
*named tuple* with the field names: "type string start end line".

The returned *named tuple* has an additional property named
"exact_type" that contains the exact operator type for "token.OP"
tokens. For all other token types "exact_type" equals the named
tuple "type" field.

Changed in version 3.1: Added support for named tuples.

Changed in version 3.3: Added support for "exact_type".

"tokenize()" determines the source encoding of the file by looking
for a UTF-8 BOM or encoding cookie, according to **PEP 263**.

All constants from the "token" module are also exported from
"tokenize", as are three additional token type values:

tokenize.COMMENT

Token value used to indicate a comment.

tokenize.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.

tokenize.ENCODING

Token value that indicates the encoding used to decode the source
bytes into text. The first token returned by "tokenize()" will
always be an ENCODING token.

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.

tokenize.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 ENCODING token, which is the
first token sequence output by "tokenize()".

"tokenize()" needs to detect the encoding of source files it
tokenizes. The function it uses to do this is available:

tokenize.detect_encoding(readline)

The "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 "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 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 "open()" to open Python source files: it uses
"detect_encoding()" to detect the file encoding.

tokenize.open(filename)

Open a file in read only mode using the encoding detected by
"detect_encoding()".

New in version 3.2.

exception tokenize.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.

Command-Line Usage
==================

New in version 3.3.

The "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:

-h, --help

show this help message and exit

-e, --exact

display token names using the exact type

If "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)

$ 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 "-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 ''