mirror of https://github.com/python/cpython
139 lines
5.2 KiB
ReStructuredText
139 lines
5.2 KiB
ReStructuredText
:mod:`tokenize` --- Tokenizer for Python source
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===============================================
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.. module:: tokenize
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:synopsis: Lexical scanner for Python source code.
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.. moduleauthor:: Ka Ping Yee
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.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
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The :mod:`tokenize` module provides a lexical scanner for Python source code,
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implemented in Python. The scanner in this module returns comments as tokens
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as well, making it useful for implementing "pretty-printers," including
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colorizers for on-screen displays.
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The primary entry point is a :term:`generator`:
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.. function:: tokenize(readline)
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The :func:`tokenize` generator requires one argument, *readline*, which
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must be a callable object which provides the same interface as the
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:meth:`readline` method of built-in file objects (see section
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:ref:`bltin-file-objects`). Each call to the function should return one
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line of input as bytes.
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The generator produces 5-tuples with these members: the token type; the
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token string; a 2-tuple ``(srow, scol)`` of ints specifying the row and
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column where the token begins in the source; a 2-tuple ``(erow, ecol)`` of
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ints specifying the row and column where the token ends in the source; and
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the line on which the token was found. The line passed (the last tuple item)
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is the *logical* line; continuation lines are included.
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:func:`tokenize` determines the source encoding of the file by looking for a
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UTF-8 BOM or encoding cookie, according to :pep:`263`.
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All constants from the :mod:`token` module are also exported from
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:mod:`tokenize`, as are three additional token type values:
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.. data:: COMMENT
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Token value used to indicate a comment.
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.. data:: NL
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Token value used to indicate a non-terminating newline. The NEWLINE token
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indicates the end of a logical line of Python code; NL tokens are generated
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when a logical line of code is continued over multiple physical lines.
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.. data:: ENCODING
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Token value that indicates the encoding used to decode the source bytes
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into text. The first token returned by :func:`tokenize` will always be an
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ENCODING token.
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Another function is provided to reverse the tokenization process. This is
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useful for creating tools that tokenize a script, modify the token stream, and
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write back the modified script.
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.. function:: untokenize(iterable)
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Converts tokens back into Python source code. The *iterable* must return
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sequences with at least two elements, the token type and the token string.
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Any additional sequence elements are ignored.
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The reconstructed script is returned as a single string. The result is
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guaranteed to tokenize back to match the input so that the conversion is
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lossless and round-trips are assured. The guarantee applies only to the
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token type and token string as the spacing between tokens (column
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positions) may change.
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It returns bytes, encoded using the ENCODING token, which is the first
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token sequence output by :func:`tokenize`.
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:func:`tokenize` needs to detect the encoding of source files it tokenizes. The
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function it uses to do this is available:
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.. function:: detect_encoding(readline)
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The :func:`detect_encoding` function is used to detect the encoding that
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should be used to decode a Python source file. It requires one argument,
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readline, in the same way as the :func:`tokenize` generator.
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It will call readline a maximum of twice, and return the encoding used
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(as a string) and a list of any lines (not decoded from bytes) it has read
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in.
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It detects the encoding from the presence of a utf-8 bom or an encoding
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cookie as specified in pep-0263. If both a bom and a cookie are present,
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but disagree, a SyntaxError will be raised.
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If no encoding is specified, then the default of 'utf-8' will be returned.
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Example of a script re-writer that transforms float literals into Decimal
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objects::
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def decistmt(s):
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"""Substitute Decimals for floats in a string of statements.
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>>> from decimal import Decimal
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>>> s = 'print(+21.3e-5*-.1234/81.7)'
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>>> decistmt(s)
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"print (+Decimal ('21.3e-5')*-Decimal ('.1234')/Decimal ('81.7'))"
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The format of the exponent is inherited from the platform C library.
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Known cases are "e-007" (Windows) and "e-07" (not Windows). Since
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we're only showing 12 digits, and the 13th isn't close to 5, the
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rest of the output should be platform-independent.
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>>> exec(s) #doctest: +ELLIPSIS
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-3.21716034272e-0...7
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Output from calculations with Decimal should be identical across all
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platforms.
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>>> exec(decistmt(s))
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-3.217160342717258261933904529E-7
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"""
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result = []
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g = tokenize(BytesIO(s.encode('utf-8')).readline) # tokenize the string
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for toknum, tokval, _, _, _ in g:
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if toknum == NUMBER and '.' in tokval: # replace NUMBER tokens
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result.extend([
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(NAME, 'Decimal'),
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(OP, '('),
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(STRING, repr(tokval)),
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(OP, ')')
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])
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else:
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result.append((toknum, tokval))
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return untokenize(result).decode('utf-8')
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