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Text File  |  2007-12-10  |  4KB  |  112 lines
  1. """ Python 'utf-8-sig' Codec
  2. This work similar to UTF-8 with the following changes:
  3.  
  4. * On encoding/writing a UTF-8 encoded BOM will be prepended/written as the
  5.   first three bytes.
  6.  
  7. * On decoding/reading if the first three bytes are a UTF-8 encoded BOM, these
  8.   bytes will be skipped.
  9. """
  10. import codecs
  11.  
  12. ### Codec APIs
  13.  
  14. def encode(input, errors='strict'):
  15.     return (codecs.BOM_UTF8 + codecs.utf_8_encode(input, errors)[0], len(input))
  16.  
  17. def decode(input, errors='strict'):
  18.     prefix = 0
  19.     if input[:3] == codecs.BOM_UTF8:
  20.         input = input[3:]
  21.         prefix = 3
  22.     (output, consumed) = codecs.utf_8_decode(input, errors, True)
  23.     return (output, consumed+prefix)
  24.  
  25. class IncrementalEncoder(codecs.IncrementalEncoder):
  26.     def __init__(self, errors='strict'):
  27.         codecs.IncrementalEncoder.__init__(self, errors)
  28.         self.first = True
  29.  
  30.     def encode(self, input, final=False):
  31.         if self.first:
  32.             self.first = False
  33.             return codecs.BOM_UTF8 + codecs.utf_8_encode(input, self.errors)[0]
  34.         else:
  35.             return codecs.utf_8_encode(input, self.errors)[0]
  36.  
  37.     def reset(self):
  38.         codecs.IncrementalEncoder.reset(self)
  39.         self.first = True
  40.  
  41. class IncrementalDecoder(codecs.BufferedIncrementalDecoder):
  42.     def __init__(self, errors='strict'):
  43.         codecs.BufferedIncrementalDecoder.__init__(self, errors)
  44.         self.first = True
  45.  
  46.     def _buffer_decode(self, input, errors, final):
  47.         if self.first:
  48.             if len(input) < 3:
  49.                 if codecs.BOM_UTF8.startswith(input):
  50.                     # not enough data to decide if this really is a BOM
  51.                     # => try again on the next call
  52.                     return (u"", 0)
  53.                 else:
  54.                     self.first = None
  55.             else:
  56.                 self.first = None
  57.                 if input[:3] == codecs.BOM_UTF8:
  58.                     (output, consumed) = codecs.utf_8_decode(input[3:], errors, final)
  59.                     return (output, consumed+3)
  60.         return codecs.utf_8_decode(input, errors, final)
  61.  
  62.     def reset(self):
  63.         codecs.BufferedIncrementalDecoder.reset(self)
  64.         self.first = True
  65.  
  66. class StreamWriter(codecs.StreamWriter):
  67.     def reset(self):
  68.         codecs.StreamWriter.reset(self)
  69.         try:
  70.             del self.encode
  71.         except AttributeError:
  72.             pass
  73.  
  74.     def encode(self, input, errors='strict'):
  75.         self.encode = codecs.utf_8_encode
  76.         return encode(input, errors)
  77.  
  78. class StreamReader(codecs.StreamReader):
  79.     def reset(self):
  80.         codecs.StreamReader.reset(self)
  81.         try:
  82.             del self.decode
  83.         except AttributeError:
  84.             pass
  85.  
  86.     def decode(self, input, errors='strict'):
  87.         if len(input) < 3:
  88.             if codecs.BOM_UTF8.startswith(input):
  89.                 # not enough data to decide if this is a BOM
  90.                 # => try again on the next call
  91.                 return (u"", 0)
  92.         elif input[:3] == codecs.BOM_UTF8:
  93.             self.decode = codecs.utf_8_decode
  94.             (output, consumed) = codecs.utf_8_decode(input[3:],errors)
  95.             return (output, consumed+3)
  96.         # (else) no BOM present
  97.         self.decode = codecs.utf_8_decode
  98.         return codecs.utf_8_decode(input, errors)
  99.  
  100. ### encodings module API
  101.  
  102. def getregentry():
  103.     return codecs.CodecInfo(
  104.         name='utf-8-sig',
  105.         encode=encode,
  106.         decode=decode,
  107.         incrementalencoder=IncrementalEncoder,
  108.         incrementaldecoder=IncrementalDecoder,
  109.         streamreader=StreamReader,
  110.         streamwriter=StreamWriter,
  111.     )
  112.