32.7. "tokenize" — Tokenizer for Python source
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**Source code:** Lib/tokenize.py

======================================================================

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.

To simplify token stream handling, all Operators and Delimiters tokens
are returned using the generic "token.OP" token type.  The exact type
can be determined by checking the second field (containing the actual
token string matched) of the tuple returned from
"tokenize.generate_tokens()" for the character sequence that
identifies a specific operator token.

The primary entry point is a *generator*:

tokenize.generate_tokens(readline)

   The "generate_tokens()" generator requires one argument,
   *readline*, which must be a callable object which provides the same
   interface as the "readline()" method of built-in file objects (see
   section 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 "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.

   New in version 2.2.

An older entry point is retained for backward compatibility:

tokenize.tokenize(readline[, tokeneater])

   The "tokenize()" function accepts two parameters: one representing
   the input stream, and one providing an output mechanism for
   "tokenize()".

   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 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 "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()":

tokenize.COMMENT

   Token value used to indicate a comment.

tokenize.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.

tokenize.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.

   New in version 2.5.

exception tokenize.TokenError

   Raised when either a docstring or expression that may be split over
   several lines is not completed anywhere in the file, for example:

      """Beginning of
      docstring

   or:

      [1,
       2,
       3

Note that unclosed single-quoted strings do not cause an error to be
raised. They are tokenized as "ERRORTOKEN", followed by the
tokenization of their contents.

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)
