"tokenize" — Tokenizer for Python source
****************************************

**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 operator and delimiter tokens
and "Ellipsis" are returned using the generic "OP" token type.  The
exact type can be determined by checking the "exact_type" property on
the *named tuple* returned from "tokenize.tokenize()".


Tokenizing Input
================

The primary entry point is a *generator*:

tokenize.tokenize(readline)

   The "tokenize()" generator requires one argument, *readline*, which
   must be a callable object which provides the same interface as the
   "io.IOBase.readline()" method of file objects.  Each call to the
   function should return one line of input as bytes.

   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 *physical*
   line.  The 5 tuple is returned as a *named tuple* with the field
   names: "type string start end line".

   The returned *named tuple* has an additional property named
   "exact_type" that contains the exact operator type for "OP" tokens.
   For all other token types "exact_type" equals the named tuple
   "type" field.

   Changed in version 3.1: Added support for named tuples.

   Changed in version 3.3: Added support for "exact_type".

   "tokenize()" determines the source encoding of the file by looking
   for a UTF-8 BOM or encoding cookie, according to **PEP 263**.

tokenize.generate_tokens(readline)

   Tokenize a source reading unicode strings instead of bytes.

   Like "tokenize()", the *readline* argument is a callable returning
   a single line of input. However, "generate_tokens()" expects
   *readline* to return a str object rather than bytes.

   The result is an iterator yielding named tuples, exactly like
   "tokenize()". It does not yield an "ENCODING" token.

All constants from the "token" module are also exported from
"tokenize".

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.

   It returns bytes, encoded using the "ENCODING" token, which is the
   first token sequence output by "tokenize()". If there is no
   encoding token in the input, it returns a str instead.

"tokenize()" needs to detect the encoding of source files it
tokenizes. The function it uses to do this is available:

tokenize.detect_encoding(readline)

   The "detect_encoding()" function is used to detect the encoding
   that should be used to decode a Python source file. It requires one
   argument, readline, in the same way as the "tokenize()" generator.

   It will call readline a maximum of twice, and return the encoding
   used (as a string) and a list of any lines (not decoded from bytes)
   it has read in.

   It detects the encoding from the presence of a UTF-8 BOM or an
   encoding cookie as specified in **PEP 263**. If both a BOM and a
   cookie are present, but disagree, a "SyntaxError" will be raised.
   Note that if the BOM is found, "'utf-8-sig'" will be returned as an
   encoding.

   If no encoding is specified, then the default of "'utf-8'" will be
   returned.

   Use "open()" to open Python source files: it uses
   "detect_encoding()" to detect the file encoding.

tokenize.open(filename)

   Open a file in read only mode using the encoding detected by
   "detect_encoding()".

   New in version 3.2.

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.


Command-Line Usage
==================

New in version 3.3.

The "tokenize" module can be executed as a script from the command
line. It is as simple as:

   python -m tokenize [-e] [filename.py]

The following options are accepted:

-h, --help

   show this help message and exit

-e, --exact

   display token names using the exact type

If "filename.py" is specified its contents are tokenized to stdout.
Otherwise, tokenization is performed on stdin.


Examples
========

Example of a script rewriter that transforms float literals into
Decimal objects:

   from tokenize import tokenize, untokenize, NUMBER, STRING, NAME, OP
   from io import BytesIO

   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'))"

       The format of the exponent is inherited from the platform C library.
       Known cases are "e-007" (Windows) and "e-07" (not Windows).  Since
       we're only showing 12 digits, and the 13th isn't close to 5, the
       rest of the output should be platform-independent.

       >>> exec(s)  #doctest: +ELLIPSIS
       -3.21716034272e-0...7

       Output from calculations with Decimal should be identical across all
       platforms.

       >>> exec(decistmt(s))
       -3.217160342717258261933904529E-7
       """
       result = []
       g = tokenize(BytesIO(s.encode('utf-8')).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).decode('utf-8')

Example of tokenizing from the command line.  The script:

   def say_hello():
       print("Hello, World!")

   say_hello()

will be tokenized to the following output where the first column is
the range of the line/column coordinates where the token is found, the
second column is the name of the token, and the final column is the
value of the token (if any)

   $ python -m tokenize hello.py
   0,0-0,0:            ENCODING       'utf-8'
   1,0-1,3:            NAME           'def'
   1,4-1,13:           NAME           'say_hello'
   1,13-1,14:          OP             '('
   1,14-1,15:          OP             ')'
   1,15-1,16:          OP             ':'
   1,16-1,17:          NEWLINE        '\n'
   2,0-2,4:            INDENT         '    '
   2,4-2,9:            NAME           'print'
   2,9-2,10:           OP             '('
   2,10-2,25:          STRING         '"Hello, World!"'
   2,25-2,26:          OP             ')'
   2,26-2,27:          NEWLINE        '\n'
   3,0-3,1:            NL             '\n'
   4,0-4,0:            DEDENT         ''
   4,0-4,9:            NAME           'say_hello'
   4,9-4,10:           OP             '('
   4,10-4,11:          OP             ')'
   4,11-4,12:          NEWLINE        '\n'
   5,0-5,0:            ENDMARKER      ''

The exact token type names can be displayed using the "-e" option:

   $ python -m tokenize -e hello.py
   0,0-0,0:            ENCODING       'utf-8'
   1,0-1,3:            NAME           'def'
   1,4-1,13:           NAME           'say_hello'
   1,13-1,14:          LPAR           '('
   1,14-1,15:          RPAR           ')'
   1,15-1,16:          COLON          ':'
   1,16-1,17:          NEWLINE        '\n'
   2,0-2,4:            INDENT         '    '
   2,4-2,9:            NAME           'print'
   2,9-2,10:           LPAR           '('
   2,10-2,25:          STRING         '"Hello, World!"'
   2,25-2,26:          RPAR           ')'
   2,26-2,27:          NEWLINE        '\n'
   3,0-3,1:            NL             '\n'
   4,0-4,0:            DEDENT         ''
   4,0-4,9:            NAME           'say_hello'
   4,9-4,10:           LPAR           '('
   4,10-4,11:          RPAR           ')'
   4,11-4,12:          NEWLINE        '\n'
   5,0-5,0:            ENDMARKER      ''

Example of tokenizing a file programmatically, reading unicode strings
instead of bytes with "generate_tokens()":

   import tokenize

   with tokenize.open('hello.py') as f:
       tokens = tokenize.generate_tokens(f.readline)
       for token in tokens:
           print(token)

Or reading bytes directly with "tokenize()":

   import tokenize

   with open('hello.py', 'rb') as f:
       tokens = tokenize.tokenize(f.readline)
       for token in tokens:
           print(token)
