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119 lines
4.6 KiB
TeX
119 lines
4.6 KiB
TeX
\section{\module{tokenize} ---
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Tokenizer for Python source}
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\declaremodule{standard}{tokenize}
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\modulesynopsis{Lexical scanner for Python source code.}
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\moduleauthor{Ka Ping Yee}{}
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\sectionauthor{Fred L. Drake, Jr.}{fdrake@acm.org}
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The \module{tokenize} module provides a lexical scanner for Python
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source code, implemented in Python. The scanner in this module
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returns comments as tokens as well, making it useful for implementing
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``pretty-printers,'' including colorizers for on-screen displays.
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The primary entry point is a generator:
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\begin{funcdesc}{generate_tokens}{readline}
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The \function{generate_tokens()} generator requires one argment,
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\var{readline}, which must be a callable object which
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provides the same interface as the \method{readline()} method of
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built-in file objects (see section~\ref{bltin-file-objects}). Each
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call to the function should return one line of input as a string.
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The generator produces 5-tuples with these members:
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the token type;
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the token string;
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a 2-tuple \code{(\var{srow}, \var{scol})} of ints specifying the
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row and column where the token begins in the source;
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a 2-tuple \code{(\var{erow}, \var{ecol})} of ints specifying the
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row and column where the token ends in the source;
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and the line on which the token was found.
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The line passed is the \emph{logical} line;
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continuation lines are included.
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\versionadded{2.2}
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\end{funcdesc}
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An older entry point is retained for backward compatibility:
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\begin{funcdesc}{tokenize}{readline\optional{, tokeneater}}
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The \function{tokenize()} function accepts two parameters: one
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representing the input stream, and one providing an output mechanism
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for \function{tokenize()}.
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The first parameter, \var{readline}, must be a callable object which
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provides the same interface as the \method{readline()} method of
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built-in file objects (see section~\ref{bltin-file-objects}). Each
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call to the function should return one line of input as a string.
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Alternately, \var{readline} may be a callable object that signals
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completion by raising \exception{StopIteration}.
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\versionchanged[Added \exception{StopIteration} support]{2.5}
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The second parameter, \var{tokeneater}, must also be a callable
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object. It is called once for each token, with five arguments,
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corresponding to the tuples generated by \function{generate_tokens()}.
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\end{funcdesc}
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All constants from the \refmodule{token} module are also exported from
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\module{tokenize}, as are two additional token type values that might be
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passed to the \var{tokeneater} function by \function{tokenize()}:
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\begin{datadesc}{COMMENT}
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Token value used to indicate a comment.
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\end{datadesc}
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\begin{datadesc}{NL}
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Token value used to indicate a non-terminating newline. The NEWLINE
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token indicates the end of a logical line of Python code; NL tokens
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are generated when a logical line of code is continued over multiple
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physical lines.
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\end{datadesc}
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Another function is provided to reverse the tokenization process.
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This is useful for creating tools that tokenize a script, modify
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the token stream, and write back the modified script.
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\begin{funcdesc}{untokenize}{iterable}
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Converts tokens back into Python source code. The \var{iterable}
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must return sequences with at least two elements, the token type and
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the token string. Any additional sequence elements are ignored.
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The reconstructed script is returned as a single string. The
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result is guaranteed to tokenize back to match the input so that
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the conversion is lossless and round-trips are assured. The
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guarantee applies only to the token type and token string as
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the spacing between tokens (column positions) may change.
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\versionadded{2.5}
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\end{funcdesc}
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Example of a script re-writer that transforms float literals into
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Decimal objects:
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\begin{verbatim}
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def decistmt(s):
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"""Substitute Decimals for floats in a string of statements.
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>>> from decimal import Decimal
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>>> s = 'print +21.3e-5*-.1234/81.7'
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>>> decistmt(s)
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"print +Decimal ('21.3e-5')*-Decimal ('.1234')/Decimal ('81.7')"
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>>> exec(s)
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-3.21716034272e-007
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>>> exec(decistmt(s))
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-3.217160342717258261933904529E-7
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"""
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result = []
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g = generate_tokens(StringIO(s).readline) # tokenize the string
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for toknum, tokval, _, _, _ in g:
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if toknum == NUMBER and '.' in tokval: # replace NUMBER tokens
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result.extend([
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(NAME, 'Decimal'),
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(OP, '('),
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(STRING, repr(tokval)),
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(OP, ')')
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])
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else:
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result.append((toknum, tokval))
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return untokenize(result)
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\end{verbatim}
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