codecs.py

""" codecs -- Python Codec Registry, API and helpers.


Written by Marc-Andre Lemburg (mal@lemburg.com).

(c) Copyright CNRI, All Rights Reserved. NO WARRANTY.

"""

importbuiltins
importsys

### Registry and builtin stateless codec functions

try:
from_codecsimport*
exceptImportErroraswhy:
raiseSystemError('Failed to load the builtin codecs: %s'%why)

__all__= ["register", "lookup", "open", "EncodedFile", "BOM", "BOM_BE",
"BOM_LE", "BOM32_BE", "BOM32_LE", "BOM64_BE", "BOM64_LE",
"BOM_UTF8", "BOM_UTF16", "BOM_UTF16_LE", "BOM_UTF16_BE",
"BOM_UTF32", "BOM_UTF32_LE", "BOM_UTF32_BE",
"CodecInfo", "Codec", "IncrementalEncoder", "IncrementalDecoder",
"StreamReader", "StreamWriter",
"StreamReaderWriter", "StreamRecoder",
"getencoder", "getdecoder", "getincrementalencoder",
"getincrementaldecoder", "getreader", "getwriter",
"encode", "decode", "iterencode", "iterdecode",
"strict_errors", "ignore_errors", "replace_errors",
"xmlcharrefreplace_errors",
"backslashreplace_errors", "namereplace_errors",
"register_error", "lookup_error"]

### Constants

#
# Byte Order Mark (BOM = ZERO WIDTH NO-BREAK SPACE = U+FEFF)
# and its possible byte string values
# for UTF8/UTF16/UTF32 output and little/big endian machines
#

# UTF-8
BOM_UTF8=b'\xef\xbb\xbf'

# UTF-16, little endian
BOM_LE=BOM_UTF16_LE=b'\xff\xfe'

# UTF-16, big endian
BOM_BE=BOM_UTF16_BE=b'\xfe\xff'

# UTF-32, little endian
BOM_UTF32_LE=b'\xff\xfe\x00\x00'

# UTF-32, big endian
BOM_UTF32_BE=b'\x00\x00\xfe\xff'

ifsys.byteorder=='little':

# UTF-16, native endianness
BOM=BOM_UTF16=BOM_UTF16_LE

# UTF-32, native endianness
BOM_UTF32=BOM_UTF32_LE

else:

# UTF-16, native endianness
BOM=BOM_UTF16=BOM_UTF16_BE

# UTF-32, native endianness
BOM_UTF32=BOM_UTF32_BE

# Old broken names (don't use in new code)
BOM32_LE=BOM_UTF16_LE
BOM32_BE=BOM_UTF16_BE
BOM64_LE=BOM_UTF32_LE
BOM64_BE=BOM_UTF32_BE


### Codec base classes (defining the API)

classCodecInfo(tuple):
"""Codec details when looking up the codec registry"""

# Private API to allow Python 3.4 to blacklist the known non-Unicode
# codecs in the standard library. A more general mechanism to
# reliably distinguish test encodings from other codecs will hopefully
# be defined for Python 3.5
#
# See http://bugs.python.org/issue19619
_is_text_encoding=True# Assume codecs are text encodings by default

def__new__(cls, encode, decode, streamreader=None, streamwriter=None,
incrementalencoder=None, incrementaldecoder=None, name=None,
*, _is_text_encoding=None):
self=tuple.__new__(cls, (encode, decode, streamreader, streamwriter))
self.name=name
self.encode=encode
self.decode=decode
self.incrementalencoder=incrementalencoder
self.incrementaldecoder=incrementaldecoder
self.streamwriter=streamwriter
self.streamreader=streamreader
if_is_text_encodingisnotNone:
self._is_text_encoding=_is_text_encoding
returnself

def__repr__(self):
return"<%s.%s object for encoding %s at %#x>"% \
 (self.__class__.__module__, self.__class__.__qualname__,
self.name, id(self))

classCodec:

""" Defines the interface for stateless encoders/decoders.

 The .encode()/.decode() methods may use different error
 handling schemes by providing the errors argument. These
 string values are predefined:

 'strict' - raise a ValueError error (or a subclass)
 'ignore' - ignore the character and continue with the next
 'replace' - replace with a suitable replacement character;
 Python will use the official U+FFFD REPLACEMENT
 CHARACTER for the builtin Unicode codecs on
 decoding and '?' on encoding.
 'surrogateescape' - replace with private code points U+DCnn.
 'xmlcharrefreplace' - Replace with the appropriate XML
 character reference (only for encoding).
 'backslashreplace' - Replace with backslashed escape sequences.
 'namereplace' - Replace with \\N{...} escape sequences
 (only for encoding).

 The set of allowed values can be extended via register_error.

 """
defencode(self, input, errors='strict'):

""" Encodes the object input and returns a tuple (output
 object, length consumed).

 errors defines the error handling to apply. It defaults to
 'strict' handling.

 The method may not store state in the Codec instance. Use
 StreamWriter for codecs which have to keep state in order to
 make encoding efficient.

 The encoder must be able to handle zero length input and
 return an empty object of the output object type in this
 situation.

 """
raiseNotImplementedError

defdecode(self, input, errors='strict'):

""" Decodes the object input and returns a tuple (output
 object, length consumed).

 input must be an object which provides the bf_getreadbuf
 buffer slot. Python strings, buffer objects and memory
 mapped files are examples of objects providing this slot.

 errors defines the error handling to apply. It defaults to
 'strict' handling.

 The method may not store state in the Codec instance. Use
 StreamReader for codecs which have to keep state in order to
 make decoding efficient.

 The decoder must be able to handle zero length input and
 return an empty object of the output object type in this
 situation.

 """
raiseNotImplementedError

classIncrementalEncoder(object):
"""
 An IncrementalEncoder encodes an input in multiple steps. The input can
 be passed piece by piece to the encode() method. The IncrementalEncoder
 remembers the state of the encoding process between calls to encode().
 """
def__init__(self, errors='strict'):
"""
 Creates an IncrementalEncoder instance.

 The IncrementalEncoder may use different error handling schemes by
 providing the errors keyword argument. See the module docstring
 for a list of possible values.
 """
self.errors=errors
self.buffer=""

defencode(self, input, final=False):
"""
 Encodes input and returns the resulting object.
 """
raiseNotImplementedError

defreset(self):
"""
 Resets the encoder to the initial state.
 """

defgetstate(self):
"""
 Return the current state of the encoder.
 """
return0

defsetstate(self, state):
"""
 Set the current state of the encoder. state must have been
 returned by getstate().
 """

classBufferedIncrementalEncoder(IncrementalEncoder):
"""
 This subclass of IncrementalEncoder can be used as the baseclass for an
 incremental encoder if the encoder must keep some of the output in a
 buffer between calls to encode().
 """
def__init__(self, errors='strict'):
IncrementalEncoder.__init__(self, errors)
# unencoded input that is kept between calls to encode()
self.buffer=""

def_buffer_encode(self, input, errors, final):
# Overwrite this method in subclasses: It must encode input
# and return an (output, length consumed) tuple
raiseNotImplementedError

defencode(self, input, final=False):
# encode input (taking the buffer into account)
data=self.buffer+input
 (result, consumed) =self._buffer_encode(data, self.errors, final)
# keep unencoded input until the next call
self.buffer=data[consumed:]
returnresult

defreset(self):
IncrementalEncoder.reset(self)
self.buffer=""

defgetstate(self):
returnself.bufferor0

defsetstate(self, state):
self.buffer=stateor""

classIncrementalDecoder(object):
"""
 An IncrementalDecoder decodes an input in multiple steps. The input can
 be passed piece by piece to the decode() method. The IncrementalDecoder
 remembers the state of the decoding process between calls to decode().
 """
def__init__(self, errors='strict'):
"""
 Create an IncrementalDecoder instance.

 The IncrementalDecoder may use different error handling schemes by
 providing the errors keyword argument. See the module docstring
 for a list of possible values.
 """
self.errors=errors

defdecode(self, input, final=False):
"""
 Decode input and returns the resulting object.
 """
raiseNotImplementedError

defreset(self):
"""
 Reset the decoder to the initial state.
 """

defgetstate(self):
"""
 Return the current state of the decoder.

 This must be a (buffered_input, additional_state_info) tuple.
 buffered_input must be a bytes object containing bytes that
 were passed to decode() that have not yet been converted.
 additional_state_info must be a non-negative integer
 representing the state of the decoder WITHOUT yet having
 processed the contents of buffered_input. In the initial state
 and after reset(), getstate() must return (b"", 0).
 """
return (b"", 0)

defsetstate(self, state):
"""
 Set the current state of the decoder.

 state must have been returned by getstate(). The effect of
 setstate((b"", 0)) must be equivalent to reset().
 """

classBufferedIncrementalDecoder(IncrementalDecoder):
"""
 This subclass of IncrementalDecoder can be used as the baseclass for an
 incremental decoder if the decoder must be able to handle incomplete
 byte sequences.
 """
def__init__(self, errors='strict'):
IncrementalDecoder.__init__(self, errors)
# undecoded input that is kept between calls to decode()
self.buffer=b""

def_buffer_decode(self, input, errors, final):
# Overwrite this method in subclasses: It must decode input
# and return an (output, length consumed) tuple
raiseNotImplementedError

defdecode(self, input, final=False):
# decode input (taking the buffer into account)
data=self.buffer+input
 (result, consumed) =self._buffer_decode(data, self.errors, final)
# keep undecoded input until the next call
self.buffer=data[consumed:]
returnresult

defreset(self):
IncrementalDecoder.reset(self)
self.buffer=b""

defgetstate(self):
# additional state info is always 0
return (self.buffer, 0)

defsetstate(self, state):
# ignore additional state info
self.buffer=state[0]

#
# The StreamWriter and StreamReader class provide generic working
# interfaces which can be used to implement new encoding submodules
# very easily. See encodings/utf_8.py for an example on how this is
# done.
#

classStreamWriter(Codec):

def__init__(self, stream, errors='strict'):

""" Creates a StreamWriter instance.

 stream must be a file-like object open for writing.

 The StreamWriter may use different error handling
 schemes by providing the errors keyword argument. These
 parameters are predefined:

 'strict' - raise a ValueError (or a subclass)
 'ignore' - ignore the character and continue with the next
 'replace'- replace with a suitable replacement character
 'xmlcharrefreplace' - Replace with the appropriate XML
 character reference.
 'backslashreplace' - Replace with backslashed escape
 sequences.
 'namereplace' - Replace with \\N{...} escape sequences.

 The set of allowed parameter values can be extended via
 register_error.
 """
self.stream=stream
self.errors=errors

defwrite(self, object):

""" Writes the object's contents encoded to self.stream.
 """
data, consumed=self.encode(object, self.errors)
self.stream.write(data)

defwritelines(self, list):

""" Writes the concatenated list of strings to the stream
 using .write().
 """
self.write(''.join(list))

defreset(self):

""" Flushes and resets the codec buffers used for keeping state.

 Calling this method should ensure that the data on the
 output is put into a clean state, that allows appending
 of new fresh data without having to rescan the whole
 stream to recover state.

 """
pass

defseek(self, offset, whence=0):
self.stream.seek(offset, whence)
ifwhence==0andoffset==0:
self.reset()

def__getattr__(self, name,
getattr=getattr):

""" Inherit all other methods from the underlying stream.
 """
returngetattr(self.stream, name)

def__enter__(self):
returnself

def__exit__(self, type, value, tb):
self.stream.close()

###

classStreamReader(Codec):

charbuffertype=str

def__init__(self, stream, errors='strict'):

""" Creates a StreamReader instance.

 stream must be a file-like object open for reading.

 The StreamReader may use different error handling
 schemes by providing the errors keyword argument. These
 parameters are predefined:

 'strict' - raise a ValueError (or a subclass)
 'ignore' - ignore the character and continue with the next
 'replace'- replace with a suitable replacement character
 'backslashreplace' - Replace with backslashed escape sequences;

 The set of allowed parameter values can be extended via
 register_error.
 """
self.stream=stream
self.errors=errors
self.bytebuffer=b""
self._empty_charbuffer=self.charbuffertype()
self.charbuffer=self._empty_charbuffer
self.linebuffer=None

defdecode(self, input, errors='strict'):
raiseNotImplementedError

defread(self, size=-1, chars=-1, firstline=False):

""" Decodes data from the stream self.stream and returns the
 resulting object.

 chars indicates the number of decoded code points or bytes to
 return. read() will never return more data than requested,
 but it might return less, if there is not enough available.

 size indicates the approximate maximum number of decoded
 bytes or code points to read for decoding. The decoder
 can modify this setting as appropriate. The default value
 -1 indicates to read and decode as much as possible. size
 is intended to prevent having to decode huge files in one
 step.

 If firstline is true, and a UnicodeDecodeError happens
 after the first line terminator in the input only the first line
 will be returned, the rest of the input will be kept until the
 next call to read().

 The method should use a greedy read strategy, meaning that
 it should read as much data as is allowed within the
 definition of the encoding and the given size, e.g. if
 optional encoding endings or state markers are available
 on the stream, these should be read too.
 """
# If we have lines cached, first merge them back into characters
ifself.linebuffer:
self.charbuffer=self._empty_charbuffer.join(self.linebuffer)
self.linebuffer=None

ifchars<0:
# For compatibility with other read() methods that take a
# single argument
chars=size

# read until we get the required number of characters (if available)
whileTrue:
# can the request be satisfied from the character buffer?
ifchars>=0:
iflen(self.charbuffer) >=chars:
break
# we need more data
ifsize<0:
newdata=self.stream.read()
else:
newdata=self.stream.read(size)
# decode bytes (those remaining from the last call included)
data=self.bytebuffer+newdata
ifnotdata:
break
try:
newchars, decodedbytes=self.decode(data, self.errors)
exceptUnicodeDecodeErrorasexc:
iffirstline:
newchars, decodedbytes= \
self.decode(data[:exc.start], self.errors)
lines=newchars.splitlines(keepends=True)
iflen(lines)<=1:
raise
else:
raise
# keep undecoded bytes until the next call
self.bytebuffer=data[decodedbytes:]
# put new characters in the character buffer
self.charbuffer+=newchars
# there was no data available
ifnotnewdata:
break
ifchars<0:
# Return everything we've got
result=self.charbuffer
self.charbuffer=self._empty_charbuffer
else:
# Return the first chars characters
result=self.charbuffer[:chars]
self.charbuffer=self.charbuffer[chars:]
returnresult

defreadline(self, size=None, keepends=True):

""" Read one line from the input stream and return the
 decoded data.

 size, if given, is passed as size argument to the
 read() method.

 """
# If we have lines cached from an earlier read, return
# them unconditionally
ifself.linebuffer:
line=self.linebuffer[0]
delself.linebuffer[0]
iflen(self.linebuffer) ==1:
# revert to charbuffer mode; we might need more data
# next time
self.charbuffer=self.linebuffer[0]
self.linebuffer=None
ifnotkeepends:
line=line.splitlines(keepends=False)[0]
returnline

readsize=sizeor72
line=self._empty_charbuffer
# If size is given, we call read() only once
whileTrue:
data=self.read(readsize, firstline=True)
ifdata:
# If we're at a "\r" read one extra character (which might
# be a "\n") to get a proper line ending. If the stream is
# temporarily exhausted we return the wrong line ending.
if (isinstance(data, str) anddata.endswith("\r")) or \
 (isinstance(data, bytes) anddata.endswith(b"\r")):
data+=self.read(size=1, chars=1)

line+=data
lines=line.splitlines(keepends=True)
iflines:
iflen(lines) >1:
# More than one line result; the first line is a full line
# to return
line=lines[0]
dellines[0]
iflen(lines) >1:
# cache the remaining lines
lines[-1] +=self.charbuffer
self.linebuffer=lines
self.charbuffer=None
else:
# only one remaining line, put it back into charbuffer
self.charbuffer=lines[0] +self.charbuffer
ifnotkeepends:
line=line.splitlines(keepends=False)[0]
break
line0withend=lines[0]
line0withoutend=lines[0].splitlines(keepends=False)[0]
ifline0withend!=line0withoutend: # We really have a line end
# Put the rest back together and keep it until the next call
self.charbuffer=self._empty_charbuffer.join(lines[1:]) + \
self.charbuffer
ifkeepends:
line=line0withend
else:
line=line0withoutend
break
# we didn't get anything or this was our only try
ifnotdataorsizeisnotNone:
iflineandnotkeepends:
line=line.splitlines(keepends=False)[0]
break
ifreadsize<8000:
readsize*=2
returnline

defreadlines(self, sizehint=None, keepends=True):

""" Read all lines available on the input stream
 and return them as a list.

 Line breaks are implemented using the codec's decoder
 method and are included in the list entries.

 sizehint, if given, is ignored since there is no efficient
 way to finding the true end-of-line.

 """
data=self.read()
returndata.splitlines(keepends)

defreset(self):

""" Resets the codec buffers used for keeping state.

 Note that no stream repositioning should take place.
 This method is primarily intended to be able to recover
 from decoding errors.

 """
self.bytebuffer=b""
self.charbuffer=self._empty_charbuffer
self.linebuffer=None

defseek(self, offset, whence=0):
""" Set the input stream's current position.

 Resets the codec buffers used for keeping state.
 """
self.stream.seek(offset, whence)
self.reset()

def__next__(self):

""" Return the next decoded line from the input stream."""
line=self.readline()
ifline:
returnline
raiseStopIteration

def__iter__(self):
returnself

def__getattr__(self, name,
getattr=getattr):

""" Inherit all other methods from the underlying stream.
 """
returngetattr(self.stream, name)

def__enter__(self):
returnself

def__exit__(self, type, value, tb):
self.stream.close()

###

classStreamReaderWriter:

""" StreamReaderWriter instances allow wrapping streams which
 work in both read and write modes.

 The design is such that one can use the factory functions
 returned by the codec.lookup() function to construct the
 instance.

 """
# Optional attributes set by the file wrappers below
encoding='unknown'

def__init__(self, stream, Reader, Writer, errors='strict'):

""" Creates a StreamReaderWriter instance.

 stream must be a Stream-like object.

 Reader, Writer must be factory functions or classes
 providing the StreamReader, StreamWriter interface resp.

 Error handling is done in the same way as defined for the
 StreamWriter/Readers.

 """
self.stream=stream
self.reader=Reader(stream, errors)
self.writer=Writer(stream, errors)
self.errors=errors

defread(self, size=-1):

returnself.reader.read(size)

defreadline(self, size=None):

returnself.reader.readline(size)

defreadlines(self, sizehint=None):

returnself.reader.readlines(sizehint)

def__next__(self):

""" Return the next decoded line from the input stream."""
returnnext(self.reader)

def__iter__(self):
returnself

defwrite(self, data):

returnself.writer.write(data)

defwritelines(self, list):

returnself.writer.writelines(list)

defreset(self):

self.reader.reset()
self.writer.reset()

defseek(self, offset, whence=0):
self.stream.seek(offset, whence)
self.reader.reset()
ifwhence==0andoffset==0:
self.writer.reset()

def__getattr__(self, name,
getattr=getattr):

""" Inherit all other methods from the underlying stream.
 """
returngetattr(self.stream, name)

# these are needed to make "with StreamReaderWriter(...)" work properly

def__enter__(self):
returnself

def__exit__(self, type, value, tb):
self.stream.close()

###

classStreamRecoder:

""" StreamRecoder instances translate data from one encoding to another.

 They use the complete set of APIs returned by the
 codecs.lookup() function to implement their task.

 Data written to the StreamRecoder is first decoded into an
 intermediate format (depending on the "decode" codec) and then
 written to the underlying stream using an instance of the provided
 Writer class.

 In the other direction, data is read from the underlying stream using
 a Reader instance and then encoded and returned to the caller.

 """
# Optional attributes set by the file wrappers below
data_encoding='unknown'
file_encoding='unknown'

def__init__(self, stream, encode, decode, Reader, Writer,
errors='strict'):

""" Creates a StreamRecoder instance which implements a two-way
 conversion: encode and decode work on the frontend (the
 data visible to .read() and .write()) while Reader and Writer
 work on the backend (the data in stream).

 You can use these objects to do transparent
 transcodings from e.g. latin-1 to utf-8 and back.

 stream must be a file-like object.

 encode and decode must adhere to the Codec interface; Reader and
 Writer must be factory functions or classes providing the
 StreamReader and StreamWriter interfaces resp.

 Error handling is done in the same way as defined for the
 StreamWriter/Readers.

 """
self.stream=stream
self.encode=encode
self.decode=decode
self.reader=Reader(stream, errors)
self.writer=Writer(stream, errors)
self.errors=errors

defread(self, size=-1):

data=self.reader.read(size)
data, bytesencoded=self.encode(data, self.errors)
returndata

defreadline(self, size=None):

ifsizeisNone:
data=self.reader.readline()
else:
data=self.reader.readline(size)
data, bytesencoded=self.encode(data, self.errors)
returndata

defreadlines(self, sizehint=None):

data=self.reader.read()
data, bytesencoded=self.encode(data, self.errors)
returndata.splitlines(keepends=True)

def__next__(self):

""" Return the next decoded line from the input stream."""
data=next(self.reader)
data, bytesencoded=self.encode(data, self.errors)
returndata

def__iter__(self):
returnself

defwrite(self, data):

data, bytesdecoded=self.decode(data, self.errors)
returnself.writer.write(data)

defwritelines(self, list):

data=b''.join(list)
data, bytesdecoded=self.decode(data, self.errors)
returnself.writer.write(data)

defreset(self):

self.reader.reset()
self.writer.reset()

defseek(self, offset, whence=0):
# Seeks must be propagated to both the readers and writers
# as they might need to reset their internal buffers.
self.reader.seek(offset, whence)
self.writer.seek(offset, whence)

def__getattr__(self, name,
getattr=getattr):

""" Inherit all other methods from the underlying stream.
 """
returngetattr(self.stream, name)

def__enter__(self):
returnself

def__exit__(self, type, value, tb):
self.stream.close()

### Shortcuts

defopen(filename, mode='r', encoding=None, errors='strict', buffering=1):

""" Open an encoded file using the given mode and return
 a wrapped version providing transparent encoding/decoding.

 Note: The wrapped version will only accept the object format
 defined by the codecs, i.e. Unicode objects for most builtin
 codecs. Output is also codec dependent and will usually be
 Unicode as well.

 Underlying encoded files are always opened in binary mode.
 The default file mode is 'r', meaning to open the file in read mode.

 encoding specifies the encoding which is to be used for the
 file.

 errors may be given to define the error handling. It defaults
 to 'strict' which causes ValueErrors to be raised in case an
 encoding error occurs.

 buffering has the same meaning as for the builtin open() API.
 It defaults to line buffered.

 The returned wrapped file object provides an extra attribute
 .encoding which allows querying the used encoding. This
 attribute is only available if an encoding was specified as
 parameter.

 """
ifencodingisnotNoneand \
'b'notinmode:
# Force opening of the file in binary mode
mode=mode+'b'
file=builtins.open(filename, mode, buffering)
ifencodingisNone:
returnfile

try:
info=lookup(encoding)
srw=StreamReaderWriter(file, info.streamreader, info.streamwriter, errors)
# Add attributes to simplify introspection
srw.encoding=encoding
returnsrw
except:
file.close()
raise

defEncodedFile(file, data_encoding, file_encoding=None, errors='strict'):

""" Return a wrapped version of file which provides transparent
 encoding translation.

 Data written to the wrapped file is decoded according
 to the given data_encoding and then encoded to the underlying
 file using file_encoding. The intermediate data type
 will usually be Unicode but depends on the specified codecs.

 Bytes read from the file are decoded using file_encoding and then
 passed back to the caller encoded using data_encoding.

 If file_encoding is not given, it defaults to data_encoding.

 errors may be given to define the error handling. It defaults
 to 'strict' which causes ValueErrors to be raised in case an
 encoding error occurs.

 The returned wrapped file object provides two extra attributes
 .data_encoding and .file_encoding which reflect the given
 parameters of the same name. The attributes can be used for
 introspection by Python programs.

 """
iffile_encodingisNone:
file_encoding=data_encoding
data_info=lookup(data_encoding)
file_info=lookup(file_encoding)
sr=StreamRecoder(file, data_info.encode, data_info.decode,
file_info.streamreader, file_info.streamwriter, errors)
# Add attributes to simplify introspection
sr.data_encoding=data_encoding
sr.file_encoding=file_encoding
returnsr

### Helpers for codec lookup

defgetencoder(encoding):

""" Lookup up the codec for the given encoding and return
 its encoder function.

 Raises a LookupError in case the encoding cannot be found.

 """
returnlookup(encoding).encode

defgetdecoder(encoding):

""" Lookup up the codec for the given encoding and return
 its decoder function.

 Raises a LookupError in case the encoding cannot be found.

 """
returnlookup(encoding).decode

defgetincrementalencoder(encoding):

""" Lookup up the codec for the given encoding and return
 its IncrementalEncoder class or factory function.

 Raises a LookupError in case the encoding cannot be found
 or the codecs doesn't provide an incremental encoder.

 """
encoder=lookup(encoding).incrementalencoder
ifencoderisNone:
raiseLookupError(encoding)
returnencoder

defgetincrementaldecoder(encoding):

""" Lookup up the codec for the given encoding and return
 its IncrementalDecoder class or factory function.

 Raises a LookupError in case the encoding cannot be found
 or the codecs doesn't provide an incremental decoder.

 """
decoder=lookup(encoding).incrementaldecoder
ifdecoderisNone: