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Module codecs -- Python Codec Registry, API and helpers. Written by
Marc-Andre Lemburg.
This commit is contained in:
Guido van Rossum
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Lib/codecs.py
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Lib/codecs.py
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""" codecs -- Python Codec Registry, API and helpers.
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Written by Marc-Andre Lemburg (mal@lemburg.com).
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(c) Copyright CNRI, All Rights Reserved. NO WARRANTY.
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"""#"
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import struct,types,__builtin__
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### Registry and builtin stateless codec functions
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from _codecs import *
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### Constants
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#
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# Byte Order Mark (BOM) and its possible values (BOM_BE, BOM_LE)
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#
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BOM = struct.pack('=H',0xFEFF)
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#
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BOM_BE = BOM32_BE = '\376\377'
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# corresponds to Unicode U+FEFF in UTF-16 on big endian
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# platforms == ZERO WIDTH NO-BREAK SPACE
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BOM_LE = BOM32_LE = '\377\376'
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# corresponds to Unicode U+FFFE in UTF-16 on little endian
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# platforms == defined as being an illegal Unicode character
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#
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# 64-bit Byte Order Marks
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#
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BOM64_BE = '\000\000\376\377'
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# corresponds to Unicode U+0000FEFF in UCS-4
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BOM64_LE = '\377\376\000\000'
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# corresponds to Unicode U+0000FFFE in UCS-4
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### Codec base classes (defining the API)
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class Codec:
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""" Defines the interface for stateless encoders/decoders.
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The .encode()/.decode() methods may implement different error
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handling schemes by providing the errors argument. These
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string values are defined:
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'strict' - raise an error (or a subclass)
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'ignore' - ignore the character and continue with the next
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'replace' - replace with a suitable replacement character;
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Python will use the official U+FFFD REPLACEMENT
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CHARACTER for the builtin Unicode codecs.
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"""
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def encode(self,input,errors='strict'):
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""" Encodes the object intput and returns a tuple (output
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object, length consumed).
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errors defines the error handling to apply. It defaults to
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'strict' handling.
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The method may not store state in the Codec instance. Use
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StreamCodec for codecs which have to keep state in order to
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make encoding/decoding efficient.
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The encoder must be able to handle zero length input and
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return an empty object of the output object type in this
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situation.
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"""
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raise NotImplementedError
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def decode(self,input,errors='strict'):
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""" Decodes the object input and returns a tuple (output
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object, length consumed).
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input must be an object which provides the bf_getreadbuf
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buffer slot. Python strings, buffer objects and memory
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mapped files are examples of objects providing this slot.
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errors defines the error handling to apply. It defaults to
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'strict' handling.
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The method may not store state in the Codec instance. Use
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StreamCodec for codecs which have to keep state in order to
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make encoding/decoding efficient.
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The decoder must be able to handle zero length input and
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return an empty object of the output object type in this
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situation.
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"""
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raise NotImplementedError
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#
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# The StreamWriter and StreamReader class provide generic working
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# interfaces which can be used to implement new encodings submodules
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# very easily. See encodings/utf_8.py for an example on how this is
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# done.
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#
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class StreamWriter(Codec):
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def __init__(self,stream,errors='strict'):
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""" Creates a StreamWriter instance.
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stream must be a file-like object open for writing
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(binary) data.
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The StreamWriter may implement different error handling
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schemes by providing the errors keyword argument. These
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parameters are defined:
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'strict' - raise a ValueError (or a subclass)
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'ignore' - ignore the character and continue with the next
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'replace'- replace with a suitable replacement character
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"""
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self.stream = stream
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self.errors = errors
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def write(self,object):
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""" Writes the object's contents encoded to self.stream.
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"""
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data, consumed = self.encode(object,self.errors)
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self.stream.write(data)
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# XXX .writelines() ?
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def reset(self):
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""" Flushes and resets the codec buffers used for keeping state.
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Calling this method should ensure that the data on the
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output is put into a clean state, that allows appending
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of new fresh data without having to rescan the whole
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stream to recover state.
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"""
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pass
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def __getattr__(self,name,
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getattr=getattr):
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""" Inherit all other methods from the underlying stream.
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"""
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return getattr(self.stream,name)
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###
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class StreamReader(Codec):
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def __init__(self,stream,errors='strict'):
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""" Creates a StreamReader instance.
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stream must be a file-like object open for reading
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(binary) data.
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The StreamReader may implement different error handling
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schemes by providing the errors keyword argument. These
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parameters are defined:
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'strict' - raise a ValueError (or a subclass)
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'ignore' - ignore the character and continue with the next
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'replace'- replace with a suitable replacement character;
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"""
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self.stream = stream
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self.errors = errors
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def read(self,size=-1):
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""" Decodes data from the stream self.stream and returns the
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resulting object.
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size indicates the approximate maximum number of bytes to
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read from the stream for decoding purposes. The decoder
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can modify this setting as appropriate. The default value
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-1 indicates to read and decode as much as possible. size
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is intended to prevent having to decode huge files in one
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step.
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The method should use a greedy read strategy meaning that
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it should read as much data as is allowed within the
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definition of the encoding and the given size, e.g. if
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optional encoding endings or state markers are available
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on the stream, these should be read too.
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"""
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# Unsliced reading:
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if size < 0:
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return self.decode(self.stream.read())[0]
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# Sliced reading:
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read = self.stream.read
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decode = self.decode
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data = read(size)
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i = 0
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while 1:
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try:
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object, decodedbytes = decode(data)
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except ValueError,why:
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# This method is slow but should work under pretty much
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# all conditions; at most 10 tries are made
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i = i + 1
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newdata = read(1)
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if not newdata or i > 10:
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raise
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data = data + newdata
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else:
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return object
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# XXX .readline() and .readlines() (these are hard to implement
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# without using buffers for keeping read-ahead data)
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def reset(self):
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""" Resets the codec buffers used for keeping state.
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Note that no stream repositioning should take place.
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This method is primarely intended to be able to recover
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from decoding errors.
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"""
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pass
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def __getattr__(self,name,
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getattr=getattr):
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""" Inherit all other methods from the underlying stream.
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"""
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return getattr(self.stream,name)
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###
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class StreamReaderWriter:
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def __init__(self,stream,Reader,Writer,errors='strict'):
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""" Creates a StreamReaderWriter instance.
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stream must be a Stream-like object.
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Reader, Writer must be factory functions or classes
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providing the StreamReader, StreamWriter interface resp.
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Error handling is done in the same way as defined for the
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StreamWriter/Readers.
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"""
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self.stream = stream
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self.reader = Reader(stream, errors)
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self.writer = Writer(stream, errors)
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self.errors = errors
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def read(self,size=-1):
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return self.reader.read(size)
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def write(self,data):
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return self.writer.write(data)
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def reset(self):
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self.reader.reset()
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self.writer.reset()
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def __getattr__(self,name,
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getattr=getattr):
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""" Inherit all other methods from the underlying stream.
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"""
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return getattr(self.stream,name)
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###
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class StreamRecoder:
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def __init__(self,stream,encode,decode,Reader,Writer,errors='strict'):
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""" Creates a StreamRecoder instance which implements a two-way
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conversion: encode and decode work on the frontend (the
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input to .read() and output of .write()) while
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Reader and Writer work on the backend (reading and
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writing to the the stream).
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You can use these objects to do transparent direct
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recodings from e.g. latin-1 to utf-8 and back.
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stream must be a file-like object.
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encode, decode must adhere to the Codec interface, Reader,
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Writer must be factory functions or classes providing the
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StreamReader, StreamWriter interface resp.
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encode and decode are needed for the frontend translation,
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Reader and Writer for the backend translation. Unicode is
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used as intermediate encoding.
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Error handling is done in the same way as defined for the
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StreamWriter/Readers.
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"""
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self.stream = stream
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self.encode = encode
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self.decode = decode
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self.reader = Reader(stream, errors)
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self.writer = Writer(stream, errors)
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self.errors = errors
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def read(self,size=-1):
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data = self.reader.read(size)
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data, bytesencoded = self.encode(data, self.errors)
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return data
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def write(self,data):
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data, bytesdecoded = self.decode(data, self.errors)
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return self.writer.write(data)
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# .writelines(), .readline() and .readlines() ... see notes
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# above.
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def reset(self):
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self.reader.reset()
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self.writer.reset()
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def __getattr__(self,name,
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getattr=getattr):
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""" Inherit all other methods from the underlying stream.
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"""
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return getattr(self.stream,name)
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### Shortcuts
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def open(filename, mode, encoding=None, errors='strict', buffering=1):
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""" Open an encoded file using the given mode and return
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a wrapped version providing transparent encoding/decoding.
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Note: The wrapped version will only accept the object format
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defined by the codecs, i.e. Unicode objects for most builtin
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codecs. Output is also codec dependent and will usually by
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Unicode as well.
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encoding specifies the encoding which is to be used for the
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the file.
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errors may be given to define the error handling. It defaults
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to 'strict' which causes ValueErrors to be raised in case an
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encoding error occurs.
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buffering has the same meaning as for the builtin open() API.
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It defaults to line buffered.
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"""
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if encoding is not None and \
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'b' not in mode:
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# Force opening of the file in binary mode
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mode = mode + 'b'
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file = __builtin__.open(filename, mode, buffering)
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if encoding is None:
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return file
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(e,d,sr,sw) = lookup(encoding)
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return StreamReaderWriter(file, sr, sw, errors)
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def EncodedFile(file, input, output=None, errors='strict'):
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""" Return a wrapped version of file which provides transparent
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encoding translation.
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Strings written to the wrapped file are interpreted according
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to the given input encoding and then written to the original
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file as string using the output encoding. The intermediate
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encoding will usually be Unicode but depends on the specified
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codecs.
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If output is not given, it defaults to input.
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errors may be given to define the error handling. It defaults
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to 'strict' which causes ValueErrors to be raised in case an
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encoding error occurs.
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"""
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if output is None:
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output = input
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encode, decode = lookup(input)[:2]
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Reader, Writer = lookup(output)[2:]
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return StreamRecoder(file,
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encode,decode,Reader,Writer,
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errors)
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### Tests
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if __name__ == '__main__':
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import sys
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# Make stdout translate Latin-1 into Unicode-Escape
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sys.stdout = EncodedFile(sys.stdout, 'latin-1', 'unicode-escape')
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