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