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""" Python 'utf-8-sig' Codec
This work similar to UTF-8 with the following changes:
* On encoding/writing a UTF-8 encoded BOM will be prepended/written as the
first three bytes.
* On decoding/reading if the first three bytes are a UTF-8 encoded BOM, these
bytes will be skipped.
"""
import codecs
### Codec APIs
def encode(input, errors='strict'):
return (codecs.BOM_UTF8 + codecs.utf_8_encode(input, errors)[0], len(input))
def decode(input, errors='strict'):
prefix = 0
if input[:3] == codecs.BOM_UTF8:
input = input[3:]
prefix = 3
(output, consumed) = codecs.utf_8_decode(input, errors, True)
return (output, consumed+prefix)
class IncrementalEncoder(codecs.IncrementalEncoder):
def __init__(self, errors='strict'):
codecs.IncrementalEncoder.__init__(self, errors)
self.first = True
def encode(self, input, final=False):
if self.first:
self.first = False
return codecs.BOM_UTF8 + codecs.utf_8_encode(input, self.errors)[0]
else:
return codecs.utf_8_encode(input, self.errors)[0]
def reset(self):
codecs.IncrementalEncoder.reset(self)
self.first = True
class IncrementalDecoder(codecs.BufferedIncrementalDecoder):
def __init__(self, errors='strict'):
codecs.BufferedIncrementalDecoder.__init__(self, errors)
self.first = True
def _buffer_decode(self, input, errors, final):
if self.first:
if len(input) < 3:
if codecs.BOM_UTF8.startswith(input):
# not enough data to decide if this really is a BOM
# => try again on the next call
return (u"", 0)
else:
self.first = None
else:
self.first = None
if input[:3] == codecs.BOM_UTF8:
(output, consumed) = codecs.utf_8_decode(input[3:], errors, final)
return (output, consumed+3)
return codecs.utf_8_decode(input, errors, final)
def reset(self):
codecs.BufferedIncrementalDecoder.reset(self)
self.first = True
class StreamWriter(codecs.StreamWriter):
def reset(self):
codecs.StreamWriter.reset(self)
try:
del self.encode
except AttributeError:
pass
def encode(self, input, errors='strict'):
self.encode = codecs.utf_8_encode
return encode(input, errors)
class StreamReader(codecs.StreamReader):
def reset(self):
codecs.StreamReader.reset(self)
try:
del self.decode
except AttributeError:
pass
def decode(self, input, errors='strict'):
if len(input) < 3 and codecs.BOM_UTF8.startswith(input):
# not enough data to decide if this is a BOM
# => try again on the next call
return (u"", 0)
self.decode = codecs.utf_8_decode
return decode(input, errors)
### encodings module API
def getregentry():
return codecs.CodecInfo(
name='utf-8-sig',
encode=encode,
decode=decode,
incrementalencoder=IncrementalEncoder,
incrementaldecoder=IncrementalDecoder,
streamreader=StreamReader,
streamwriter=StreamWriter,
)
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