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342 lines
10 KiB
Python
342 lines
10 KiB
Python
# coding: utf-8
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"""
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webencodings
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~~~~~~~~~~~~
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This is a Python implementation of the `WHATWG Encoding standard
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<http://encoding.spec.whatwg.org/>`. See README for details.
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:copyright: Copyright 2012 by Simon Sapin
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:license: BSD, see LICENSE for details.
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"""
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from __future__ import unicode_literals
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import codecs
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from .labels import LABELS
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VERSION = '0.5.1'
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# Some names in Encoding are not valid Python aliases. Remap these.
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PYTHON_NAMES = {
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'iso-8859-8-i': 'iso-8859-8',
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'x-mac-cyrillic': 'mac-cyrillic',
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'macintosh': 'mac-roman',
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'windows-874': 'cp874'}
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CACHE = {}
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def ascii_lower(string):
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r"""Transform (only) ASCII letters to lower case: A-Z is mapped to a-z.
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:param string: An Unicode string.
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:returns: A new Unicode string.
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This is used for `ASCII case-insensitive
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<http://encoding.spec.whatwg.org/#ascii-case-insensitive>`_
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matching of encoding labels.
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The same matching is also used, among other things,
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for `CSS keywords <http://dev.w3.org/csswg/css-values/#keywords>`_.
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This is different from the :meth:`~py:str.lower` method of Unicode strings
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which also affect non-ASCII characters,
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sometimes mapping them into the ASCII range:
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>>> keyword = u'Bac\N{KELVIN SIGN}ground'
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>>> assert keyword.lower() == u'background'
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>>> assert ascii_lower(keyword) != keyword.lower()
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>>> assert ascii_lower(keyword) == u'bac\N{KELVIN SIGN}ground'
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"""
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# This turns out to be faster than unicode.translate()
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return string.encode('utf8').lower().decode('utf8')
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def lookup(label):
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"""
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Look for an encoding by its label.
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This is the spec’s `get an encoding
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<http://encoding.spec.whatwg.org/#concept-encoding-get>`_ algorithm.
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Supported labels are listed there.
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:param label: A string.
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:returns:
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An :class:`Encoding` object, or :obj:`None` for an unknown label.
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"""
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# Only strip ASCII whitespace: U+0009, U+000A, U+000C, U+000D, and U+0020.
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label = ascii_lower(label.strip('\t\n\f\r '))
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name = LABELS.get(label)
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if name is None:
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return None
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encoding = CACHE.get(name)
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if encoding is None:
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if name == 'x-user-defined':
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from .x_user_defined import codec_info
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else:
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python_name = PYTHON_NAMES.get(name, name)
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# Any python_name value that gets to here should be valid.
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codec_info = codecs.lookup(python_name)
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encoding = Encoding(name, codec_info)
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CACHE[name] = encoding
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return encoding
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def _get_encoding(encoding_or_label):
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"""
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Accept either an encoding object or label.
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:param encoding: An :class:`Encoding` object or a label string.
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:returns: An :class:`Encoding` object.
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:raises: :exc:`~exceptions.LookupError` for an unknown label.
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"""
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if hasattr(encoding_or_label, 'codec_info'):
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return encoding_or_label
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encoding = lookup(encoding_or_label)
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if encoding is None:
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raise LookupError('Unknown encoding label: %r' % encoding_or_label)
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return encoding
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class Encoding(object):
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"""Reresents a character encoding such as UTF-8,
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that can be used for decoding or encoding.
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.. attribute:: name
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Canonical name of the encoding
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.. attribute:: codec_info
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The actual implementation of the encoding,
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a stdlib :class:`~codecs.CodecInfo` object.
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See :func:`codecs.register`.
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"""
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def __init__(self, name, codec_info):
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self.name = name
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self.codec_info = codec_info
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def __repr__(self):
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return '<Encoding %s>' % self.name
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#: The UTF-8 encoding. Should be used for new content and formats.
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UTF8 = lookup('utf-8')
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_UTF16LE = lookup('utf-16le')
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_UTF16BE = lookup('utf-16be')
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def decode(input, fallback_encoding, errors='replace'):
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"""
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Decode a single string.
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:param input: A byte string
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:param fallback_encoding:
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An :class:`Encoding` object or a label string.
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The encoding to use if :obj:`input` does note have a BOM.
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:param errors: Type of error handling. See :func:`codecs.register`.
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:raises: :exc:`~exceptions.LookupError` for an unknown encoding label.
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:return:
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A ``(output, encoding)`` tuple of an Unicode string
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and an :obj:`Encoding`.
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"""
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# Fail early if `encoding` is an invalid label.
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fallback_encoding = _get_encoding(fallback_encoding)
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bom_encoding, input = _detect_bom(input)
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encoding = bom_encoding or fallback_encoding
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return encoding.codec_info.decode(input, errors)[0], encoding
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def _detect_bom(input):
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"""Return (bom_encoding, input), with any BOM removed from the input."""
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if input.startswith(b'\xFF\xFE'):
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return _UTF16LE, input[2:]
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if input.startswith(b'\xFE\xFF'):
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return _UTF16BE, input[2:]
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if input.startswith(b'\xEF\xBB\xBF'):
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return UTF8, input[3:]
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return None, input
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def encode(input, encoding=UTF8, errors='strict'):
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"""
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Encode a single string.
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:param input: An Unicode string.
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:param encoding: An :class:`Encoding` object or a label string.
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:param errors: Type of error handling. See :func:`codecs.register`.
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:raises: :exc:`~exceptions.LookupError` for an unknown encoding label.
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:return: A byte string.
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"""
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return _get_encoding(encoding).codec_info.encode(input, errors)[0]
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def iter_decode(input, fallback_encoding, errors='replace'):
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"""
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"Pull"-based decoder.
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:param input:
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An iterable of byte strings.
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The input is first consumed just enough to determine the encoding
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based on the precense of a BOM,
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then consumed on demand when the return value is.
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:param fallback_encoding:
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An :class:`Encoding` object or a label string.
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The encoding to use if :obj:`input` does note have a BOM.
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:param errors: Type of error handling. See :func:`codecs.register`.
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:raises: :exc:`~exceptions.LookupError` for an unknown encoding label.
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:returns:
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An ``(output, encoding)`` tuple.
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:obj:`output` is an iterable of Unicode strings,
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:obj:`encoding` is the :obj:`Encoding` that is being used.
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"""
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decoder = IncrementalDecoder(fallback_encoding, errors)
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generator = _iter_decode_generator(input, decoder)
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encoding = next(generator)
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return generator, encoding
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def _iter_decode_generator(input, decoder):
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"""Return a generator that first yields the :obj:`Encoding`,
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then yields output chukns as Unicode strings.
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"""
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decode = decoder.decode
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input = iter(input)
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for chunck in input:
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output = decode(chunck)
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if output:
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assert decoder.encoding is not None
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yield decoder.encoding
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yield output
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break
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else:
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# Input exhausted without determining the encoding
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output = decode(b'', final=True)
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assert decoder.encoding is not None
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yield decoder.encoding
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if output:
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yield output
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return
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for chunck in input:
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output = decode(chunck)
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if output:
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yield output
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output = decode(b'', final=True)
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if output:
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yield output
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def iter_encode(input, encoding=UTF8, errors='strict'):
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"""
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“Pull”-based encoder.
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:param input: An iterable of Unicode strings.
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:param encoding: An :class:`Encoding` object or a label string.
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:param errors: Type of error handling. See :func:`codecs.register`.
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:raises: :exc:`~exceptions.LookupError` for an unknown encoding label.
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:returns: An iterable of byte strings.
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"""
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# Fail early if `encoding` is an invalid label.
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encode = IncrementalEncoder(encoding, errors).encode
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return _iter_encode_generator(input, encode)
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def _iter_encode_generator(input, encode):
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for chunck in input:
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output = encode(chunck)
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if output:
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yield output
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output = encode('', final=True)
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if output:
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yield output
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class IncrementalDecoder(object):
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"""
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“Push”-based decoder.
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:param fallback_encoding:
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An :class:`Encoding` object or a label string.
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The encoding to use if :obj:`input` does note have a BOM.
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:param errors: Type of error handling. See :func:`codecs.register`.
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:raises: :exc:`~exceptions.LookupError` for an unknown encoding label.
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"""
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def __init__(self, fallback_encoding, errors='replace'):
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# Fail early if `encoding` is an invalid label.
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self._fallback_encoding = _get_encoding(fallback_encoding)
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self._errors = errors
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self._buffer = b''
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self._decoder = None
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#: The actual :class:`Encoding` that is being used,
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#: or :obj:`None` if that is not determined yet.
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#: (Ie. if there is not enough input yet to determine
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#: if there is a BOM.)
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self.encoding = None # Not known yet.
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def decode(self, input, final=False):
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"""Decode one chunk of the input.
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:param input: A byte string.
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:param final:
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Indicate that no more input is available.
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Must be :obj:`True` if this is the last call.
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:returns: An Unicode string.
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"""
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decoder = self._decoder
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if decoder is not None:
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return decoder(input, final)
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input = self._buffer + input
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encoding, input = _detect_bom(input)
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if encoding is None:
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if len(input) < 3 and not final: # Not enough data yet.
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self._buffer = input
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return ''
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else: # No BOM
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encoding = self._fallback_encoding
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decoder = encoding.codec_info.incrementaldecoder(self._errors).decode
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self._decoder = decoder
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self.encoding = encoding
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return decoder(input, final)
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class IncrementalEncoder(object):
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"""
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“Push”-based encoder.
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:param encoding: An :class:`Encoding` object or a label string.
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:param errors: Type of error handling. See :func:`codecs.register`.
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:raises: :exc:`~exceptions.LookupError` for an unknown encoding label.
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.. method:: encode(input, final=False)
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:param input: An Unicode string.
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:param final:
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Indicate that no more input is available.
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Must be :obj:`True` if this is the last call.
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:returns: A byte string.
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"""
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def __init__(self, encoding=UTF8, errors='strict'):
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encoding = _get_encoding(encoding)
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self.encode = encoding.codec_info.incrementalencoder(errors).encode
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