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 tokensas well, making it useful for implementing "pretty-printers," includingcolorizers for on-screen displays.

To simplify token stream handling, all operator anddelimiter tokens and Ellipsis are returned usingthe generic OP token type. The exacttype can be determined by checking the exact_type property on thenamed tuple returned from tokenize.tokenize().

Tokenizing Input

The primary entry point is a generator:

  • tokenize.tokenize(readline)
  • The tokenize() generator requires one argument, readline, whichmust be a callable object which provides the same interface as theio.IOBase.readline() method of file objects. Each call to thefunction should return one line of input as bytes.

The generator produces 5-tuples with these members: the token type; thetoken string; a 2-tuple (srow, scol) of ints specifying the row andcolumn where the token begins in the source; a 2-tuple (erow, ecol) ofints specifying the row and column where the token ends in the source; andthe 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 tuplewith the field names:type string start end line.

The returned named tuple has an additional property namedexact_type that contains the exact operator type forOP tokens. For all other token types exact_typeequals the named tuple type field.

在 3.1 版更改: Added support for named tuples.

在 3.3 版更改: Added support for exact_type.

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

  • tokenize.generatetokens(_readline)
  • Tokenize a source reading unicode strings instead of bytes.

Like tokenize(), the readline argument is a callable returninga 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 liketokenize(). It does not yield an ENCODING token.

All constants from the token module are also exported fromtokenize.

Another function is provided to reverse the tokenization process. This isuseful for creating tools that tokenize a script, modify the token stream, andwrite back the modified script.

  • tokenize.untokenize(iterable)
  • Converts tokens back into Python source code. The iterable must returnsequences 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 isguaranteed to tokenize back to match the input so that the conversion islossless and round-trips are assured. The guarantee applies only to thetoken type and token string as the spacing between tokens (columnpositions) may change.

It returns bytes, encoded using the ENCODING token, whichis the first token sequence output by tokenize(). If there is noencoding token in the input, it returns a str instead.

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

  • tokenize.detectencoding(_readline)
  • The detect_encoding() function is used to detect the encoding thatshould 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 readin.

It detects the encoding from the presence of a UTF-8 BOM or an encodingcookie 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 bereturned.

Use open() to open Python source files: it usesdetect_encoding() to detect the file encoding.

  • tokenize.open(filename)
  • Open a file in read only mode using the encoding detected bydetect_encoding().

3.2 新版功能.

  • exception tokenize.TokenError
  • Raised when either a docstring or expression that may be split over severallines is not completed anywhere in the file, for example:
  1. """Beginning of
  2. docstring

或者：

  1. [1,
  2.  2,
  3.  3

Note that unclosed single-quoted strings do not cause an error to beraised. They are tokenized as ERRORTOKEN, followed by thetokenization of their contents.

Command-Line Usage

3.3 新版功能.

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

  1. 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.

示例

Example of a script rewriter that transforms float literals into Decimalobjects:

  1. from tokenize import tokenize, untokenize, NUMBER, STRING, NAME, OP
  2. from io import BytesIO
  3.  
  4. def decistmt(s):
  5.     """Substitute Decimals for floats in a string of statements.
  6.  
  7.     >>> from decimal import Decimal
  8.     >>> s = 'print(+21.3e-5*-.1234/81.7)'
  9.     >>> decistmt(s)
  10.     "print (+Decimal ('21.3e-5')*-Decimal ('.1234')/Decimal ('81.7'))"
  11.  
  12.     The format of the exponent is inherited from the platform C library.
  13.     Known cases are "e-007" (Windows) and "e-07" (not Windows).  Since
  14.     we're only showing 12 digits, and the 13th isn't close to 5, the
  15.     rest of the output should be platform-independent.
  16.  
  17.     >>> exec(s)  #doctest: +ELLIPSIS
  18.     -3.21716034272e-0...7
  19.  
  20.     Output from calculations with Decimal should be identical across all
  21.     platforms.
  22.  
  23.     >>> exec(decistmt(s))
  24.     -3.217160342717258261933904529E-7
  25.     """
  26.     result = []
  27.     g = tokenize(BytesIO(s.encode('utf-8')).readline)  # tokenize the string
  28.     for toknum, tokval, _, _, _ in g:
  29.         if toknum == NUMBER and '.' in tokval:  # replace NUMBER tokens
  30.             result.extend([
  31.                 (NAME, 'Decimal'),
  32.                 (OP, '('),
  33.                 (STRING, repr(tokval)),
  34.                 (OP, ')')
  35.             ])
  36.         else:
  37.             result.append((toknum, tokval))
  38.     return untokenize(result).decode('utf-8')

Example of tokenizing from the command line. The script:

  1. def say_hello():
  2.     print("Hello, World!")
  3.  
  4. say_hello()

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

  1. $ python -m tokenize hello.py
  2. 0,0-0,0:            ENCODING       'utf-8'
  3. 1,0-1,3:            NAME           'def'
  4. 1,4-1,13:           NAME           'say_hello'
  5. 1,13-1,14:          OP             '('
  6. 1,14-1,15:          OP             ')'
  7. 1,15-1,16:          OP             ':'
  8. 1,16-1,17:          NEWLINE        '\n'
  9. 2,0-2,4:            INDENT         '    '
  10. 2,4-2,9:            NAME           'print'
  11. 2,9-2,10:           OP             '('
  12. 2,10-2,25:          STRING         '"Hello, World!"'
  13. 2,25-2,26:          OP             ')'
  14. 2,26-2,27:          NEWLINE        '\n'
  15. 3,0-3,1:            NL             '\n'
  16. 4,0-4,0:            DEDENT         ''
  17. 4,0-4,9:            NAME           'say_hello'
  18. 4,9-4,10:           OP             '('
  19. 4,10-4,11:          OP             ')'
  20. 4,11-4,12:          NEWLINE        '\n'
  21. 5,0-5,0:            ENDMARKER      ''

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

  1. $ python -m tokenize -e hello.py
  2. 0,0-0,0:            ENCODING       'utf-8'
  3. 1,0-1,3:            NAME           'def'
  4. 1,4-1,13:           NAME           'say_hello'
  5. 1,13-1,14:          LPAR           '('
  6. 1,14-1,15:          RPAR           ')'
  7. 1,15-1,16:          COLON          ':'
  8. 1,16-1,17:          NEWLINE        '\n'
  9. 2,0-2,4:            INDENT         '    '
  10. 2,4-2,9:            NAME           'print'
  11. 2,9-2,10:           LPAR           '('
  12. 2,10-2,25:          STRING         '"Hello, World!"'
  13. 2,25-2,26:          RPAR           ')'
  14. 2,26-2,27:          NEWLINE        '\n'
  15. 3,0-3,1:            NL             '\n'
  16. 4,0-4,0:            DEDENT         ''
  17. 4,0-4,9:            NAME           'say_hello'
  18. 4,9-4,10:           LPAR           '('
  19. 4,10-4,11:          RPAR           ')'
  20. 4,11-4,12:          NEWLINE        '\n'
  21. 5,0-5,0:            ENDMARKER      ''