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\section{\module{tokenize} ---
Tokenizer for Python source}
\declaremodule{standard}{tokenize}
\modulesynopsis{Lexical scanner for Python source code.}
\moduleauthor{Ka Ping Yee}{}
\sectionauthor{Fred L. Drake, Jr.}{fdrake@acm.org}
The \module{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:
\begin{funcdesc}{generate_tokens}{readline}
The \function{generate_tokens()} generator requires one argment,
\var{readline}, which must be a callable object which
provides the same interface as the \method{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 \code{(\var{srow}, \var{scol})} of ints specifying the
row and column where the token begins in the source;
a 2-tuple \code{(\var{erow}, \var{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 \emph{logical} line;
continuation lines are included.
\versionadded{2.2}
\end{funcdesc}
An older entry point is retained for backward compatibility:
\begin{funcdesc}{tokenize}{readline\optional{, tokeneater}}
The \function{tokenize()} function accepts two parameters: one
representing the input stream, and one providing an output mechanism
for \function{tokenize()}.
The first parameter, \var{readline}, must be a callable object which
provides the same interface as the \method{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, \var{readline} may be a callable object that signals
completion by raising \exception{StopIteration}.
\versionchanged[Added \exception{StopIteration} support]{2.5}
The second parameter, \var{tokeneater}, must also be a callable
object. It is called once for each token, with five arguments,
corresponding to the tuples generated by \function{generate_tokens()}.
\end{funcdesc}
All constants from the \refmodule{token} module are also exported from
\module{tokenize}, as are two additional token type values that might be
passed to the \var{tokeneater} function by \function{tokenize()}:
\begin{datadesc}{COMMENT}
Token value used to indicate a comment.
\end{datadesc}
\begin{datadesc}{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.
\end{datadesc}
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.
\begin{funcdesc}{untokenize}{iterable}
Converts tokens back into Python source code. The \var{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}
\end{funcdesc}
Example of a script re-writer that transforms float literals into
Decimal objects:
\begin{verbatim}
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)
\end{verbatim}
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