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:
The generator produces 5-tuples with these members:
the token type;
the token string;
(srow, scol) of ints specifying the
row and column where the token begins in the source;
(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 is the logical line;
continuation lines are included.
New in version 2.2.
An older entry point is retained for backward compatibility:
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 3.9). 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: 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():
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.
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.
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)