# `tokenize` --- 对 Python 代码使用的标记解析器

源码： 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.

为了简化标记流的处理，所有的 运算符 和 定界符 以及 `Ellipsis` 返回时都会打上通用的 `OP` 标记。 可以通过 `tokenize.tokenize()` 返回的 named tuple 对象的 `exact_type` 属性来获得确切的标记类型。

## 对输入进行解析标记

主要的入口是一个生成器 generator:

`tokenize.``tokenize`(readline)

  生成器 `tokenize()` 需要一个 readline 参数，这个参数必须是一个可调用对象，且能提供与文件对象的 `io.IOBase.readline()` 方法相同的接口。每次调用这个函数都要 返回字节类型输入的一行数据。

  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.

  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 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()`.

  3.2 新版功能.

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

  或者：

      [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

3.3 新版功能.

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.

## 示例

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)

或者通过 `tokenize()` 直接读取字节数据:

    import tokenize

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