/Doc/library/tokenize.rst
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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>
- 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.
- 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.
- 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)