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100 lines
3.1 KiB
Python
100 lines
3.1 KiB
Python
""" Python 'utf-8-sig' Codec
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This work similar to UTF-8 with the following changes:
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* On encoding/writing a UTF-8 encoded BOM will be prepended/written as the
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first three bytes.
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* On decoding/reading if the first three bytes are a UTF-8 encoded BOM, these
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bytes will be skipped.
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"""
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import codecs
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### Codec APIs
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def encode(input, errors='strict'):
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return (codecs.BOM_UTF8 + codecs.utf_8_encode(input, errors)[0], len(input))
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def decode(input, errors='strict'):
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prefix = 0
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if input.startswith(codecs.BOM_UTF8):
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input = input[3:]
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prefix = 3
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(output, consumed) = codecs.utf_8_decode(input, errors, True)
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return (output, consumed+prefix)
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class IncrementalEncoder(codecs.IncrementalEncoder):
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def __init__(self, errors='strict'):
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codecs.IncrementalEncoder.__init__(self, errors)
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self.first = True
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def encode(self, input, final=False):
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if self.first:
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self.first = False
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return codecs.BOM_UTF8 + codecs.utf_8_encode(input, self.errors)[0]
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else:
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return codecs.utf_8_encode(input, self.errors)[0]
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def reset(self):
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codecs.IncrementalEncoder.reset(self)
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self.first = True
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class IncrementalDecoder(codecs.BufferedIncrementalDecoder):
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def __init__(self, errors='strict'):
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codecs.BufferedIncrementalDecoder.__init__(self, errors)
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self.first = True
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def _buffer_decode(self, input, errors, final):
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if self.first and codecs.BOM_UTF8.startswith(input): # might be a BOM
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if len(input) < 3:
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# not enough data to decide if this really is a BOM
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# => try again on the next call
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return (u"", 0)
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(output, consumed) = codecs.utf_8_decode(input[3:], errors, final)
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self.first = False
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return (output, consumed+3)
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return codecs.utf_8_decode(input, errors, final)
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def reset(self):
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codecs.BufferedIncrementalDecoder.reset(self)
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self.first = True
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class StreamWriter(codecs.StreamWriter):
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def reset(self):
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codecs.StreamWriter.reset(self)
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try:
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del self.encode
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except AttributeError:
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pass
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def encode(self, input, errors='strict'):
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self.encode = codecs.utf_8_encode
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return encode(input, errors)
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class StreamReader(codecs.StreamReader):
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def reset(self):
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codecs.StreamReader.reset(self)
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try:
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del self.decode
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except AttributeError:
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pass
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def decode(self, input, errors='strict'):
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if len(input) < 3 and codecs.BOM_UTF8.startswith(input):
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# not enough data to decide if this is a BOM
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# => try again on the next call
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return (u"", 0)
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self.decode = codecs.utf_8_decode
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return decode(input, errors)
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### encodings module API
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def getregentry():
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return codecs.CodecInfo(
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name='utf-8-sig',
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encode=encode,
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decode=decode,
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incrementalencoder=IncrementalEncoder,
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incrementaldecoder=IncrementalDecoder,
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streamreader=StreamReader,
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streamwriter=StreamWriter,
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)
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