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: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:`operators` and :ref:`delimiters` tokens are returned using the generic :data:`token.OP` token type. The exact type can be determined by checking the token ``string`` field on the :term:`named tuple` returned from :func:`tokenize.tokenize` for the character sequence that identifies a specific operator token. The primary entry point is a :term:`generator`: .. function:: generate_tokens(readline) The :func:`generate_tokens` generator requires one argument, *readline*, which must be a callable object which provides the same interface as the :meth:`readline` method of built-in file objects (see section :ref:`bltin-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 :exc:`StopIteration`. 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. .. versionadded:: 2.2 An older entry point is retained for backward compatibility: .. function:: tokenize(readline[, tokeneater]) The :func:`tokenize` function accepts two parameters: one representing the input stream, and one providing an output mechanism for :func:`tokenize`. The first parameter, *readline*, must be a callable object which provides the same interface as the :meth:`readline` method of built-in file objects (see section :ref:`bltin-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 :exc:`StopIteration`. .. versionchanged:: 2.5 Added :exc:`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 :func:`generate_tokens`. All constants from the :mod:`token` module are also exported from :mod:`tokenize`, as are two additional token type values that might be passed to the *tokeneater* function by :func:`tokenize`: .. data:: COMMENT Token value used to indicate a comment. .. data:: 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. .. 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. .. versionadded:: 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)