cpython/Lib/codecs.py

415 lines
12 KiB
Python
Raw Normal View History

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