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 TokenInfo objects.

Changed in version 3.1: Changed to yield TokenInfo objects instead of plain tuples.

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

tokenize.generate_tokens(readline)¶

Tokenize a source reading unicode strings instead of bytes.

Like tokenize(), the readline argument is a callable returning a single line of input. However, generate_tokens() expects readline to return a str object rather than bytes.

The result is an iterator yielding TokenInfo objects, exactly like tokenize(). It does not yield an ENCODING token.

class tokenize.TokenInfo(type, string, start, end, line)¶

A named tuple describing a token. It has five fields and an additional exact_type property.

Added in version 3.1.

type¶

An integer identifying the token type, as defined by the constants in token, such as NAME and STRING. Operators and delimiters have type OP; use exact_type for their specific token type.

string¶

The token text as a str. For STRING tokens, this includes the quotes, any prefix, and escape sequences, without evaluating them.

For an ENCODING token, this is the encoding name. Tokens inserted without corresponding source text can have an empty string. In FSTRING_MIDDLE and TSTRING_MIDDLE tokens, doubled braces are replaced by single braces.

start¶

A 2-tuple (srow, scol) of ints specifying the inclusive start position of the token in the source. Rows are numbered from 1 and columns from 0. Columns count Unicode code points; a tab counts as one column, without expanding it to a tab stop.

For an ENCODING token, this is (0, 0).

end¶

A 2-tuple (erow, ecol) of ints specifying the exclusive end position of the token. Rows are numbered from 1 and columns from 0. For a token spanning multiple lines, erow is the final row and ecol is the column on that row.

For example, the name spam at the beginning of the first line has start equal to (1, 0) and end equal to (1, 4).

For an ENCODING token, this is (0, 0). A NEWLINE or NL token inserted at the end of input without a final newline can have an end column one beyond the source text.

line¶

A str containing the full source line on which the token was found, including surrounding text and the line terminator if present. For a token spanning multiple lines, this can contain several source lines. It is empty for ENCODING and ENDMARKER tokens.

exact_type¶

An integer identifying the specific operator type for OP tokens, as defined by the constants in token. For all other token types, this equals type. For example, a + token has type equal to OP and exact_type equal to PLUS.

Added in version 3.3.

All constants from the token module are also exported from 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.

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 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(). If there is no encoding token in the input, it returns a str instead.

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().

Added 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

Command-line usage¶

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      ''

Example of tokenizing a file programmatically, reading unicode strings instead of bytes with 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 tokenize():

import tokenize

with open('hello.py', 'rb') as f:
    tokens = tokenize.tokenize(f.readline)
    for token in tokens:
        print(token)