31.7. tokenize — Tokenizer for Python source
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.
The primary entry point is a generator:
-
tokenize.generate_tokens(readline)
The generate_tokens() generator requires one argument, readline,
which must be a callable object which provides the same interface as the
readline() method of built-in file objects (see section
File Objects). Each call to the function should return one line
of input as a string.
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.
New in version 2.2:
New in version 2.2.
An older entry point is retained for backward compatibility:
-
tokenize.tokenize(readline[, tokeneater])
The tokenize() function accepts two parameters: one representing the input
stream, and one providing an output mechanism for tokenize().
The first parameter, readline, must be a callable object which provides the
same interface as the readline() method of built-in file objects (see
section 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 StopIteration.
Changed in version 2.5:
Changed in version 2.5: Added 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 generate_tokens().
All constants from the token module are also exported from
tokenize, as are two additional token type values that might be passed to
the tokeneater function by tokenize():
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.
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.
New in version 2.5:
New in version 2.5.
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)