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cpython/Lib/codecs.py
Marc-André Lemburg d594849c42 Ignore sizehint argument. Fixes SF #844561.
2004-02-26 15:22:17 +00:00

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""" codecs -- Python Codec Registry, API and helpers.
Written by Marc-Andre Lemburg (mal@lemburg.com).
(c) Copyright CNRI, All Rights Reserved. NO WARRANTY.
"""#"
import __builtin__, sys
### Registry and builtin stateless codec functions
try:
from _codecs import *
except ImportError, why:
raise SystemError,\
'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",
"strict_errors", "ignore_errors", "replace_errors",
"xmlcharrefreplace_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 = '\xef\xbb\xbf'
# UTF-16, little endian
BOM_LE = BOM_UTF16_LE = '\xff\xfe'
# UTF-16, big endian
BOM_BE = BOM_UTF16_BE = '\xfe\xff'
# UTF-32, little endian
BOM_UTF32_LE = '\xff\xfe\x00\x00'
# UTF-32, big endian
BOM_UTF32_BE = '\x00\x00\xfe\xff'
if sys.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)
class Codec:
""" 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.
'xmlcharrefreplace' - Replace with the appropriate XML
character reference (only for encoding).
'backslashreplace' - Replace with backslashed escape sequences
(only for encoding).
The set of allowed values can be extended via register_error.
"""
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 encoding 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 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 (only for encoding).
The set of allowed parameter values can be extended via
register_error.
"""
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)
def writelines(self, list):
""" Writes the concatenated list of strings to the stream
using .write().
"""
self.write(''.join(list))
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 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;
The set of allowed parameter values can be extended via
register_error.
"""
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(), self.errors)[0]
# Sliced reading:
read = self.stream.read
decode = self.decode
data = read(size)
i = 0
while 1:
try:
object, decodedbytes = decode(data, self.errors)
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
def readline(self, size=None):
""" Read one line from the input stream and return the
decoded data.
Note: Unlike the .readlines() method, this method inherits
the line breaking knowledge from the underlying stream's
.readline() method -- there is currently no support for
line breaking using the codec decoder due to lack of line
buffering. Subclasses should however, if possible, try to
implement this method using their own knowledge of line
breaking.
size, if given, is passed as size argument to the stream's
.readline() method.
"""
if size is None:
line = self.stream.readline()
else:
line = self.stream.readline(size)
return self.decode(line, self.errors)[0]
def readlines(self, sizehint=None):
""" Read all lines available on the input stream
and return them as list of lines.
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.stream.read()
return self.decode(data, self.errors)[0].splitlines(1)
def reset(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.
"""
pass
def next(self):
""" Return the next decoded line from the input stream."""
line = self.readline()
if line:
return line
raise StopIteration
def __iter__(self):
return self
def __getattr__(self, name,
getattr=getattr):
""" Inherit all other methods from the underlying stream.
"""
return getattr(self.stream, name)
###
class StreamReaderWriter:
""" 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
def read(self, size=-1):
return self.reader.read(size)
def readline(self, size=None):
return self.reader.readline(size)
def readlines(self, sizehint=None):
return self.reader.readlines(sizehint)
def next(self):
""" Return the next decoded line from the input stream."""
return self.reader.next()
def __iter__(self):
return self
def write(self, data):
return self.writer.write(data)
def writelines(self, list):
return self.writer.writelines(list)
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:
""" StreamRecoder instances provide a frontend - backend
view of encoding data.
They use the complete set of APIs returned by the
codecs.lookup() function to implement their task.
Data written to the stream is first decoded into an
intermediate format (which is dependent on the given codec
combination) and then written to the stream using an instance
of the provided Writer class.
In the other direction, data is read from the stream using a
Reader instance and then return encoded data 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
input to .read() and output of .write()) while
Reader and Writer work on the backend (reading and
writing to 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 readline(self, size=None):
if size is None:
data = self.reader.readline()
else:
data = self.reader.readline(size)
data, bytesencoded = self.encode(data, self.errors)
return data
def readlines(self, sizehint=None):
data = self.reader.read()
data, bytesencoded = self.encode(data, self.errors)
return data.splitlines(1)
def next(self):
""" Return the next decoded line from the input stream."""
return self.reader.next()
def __iter__(self):
return self
def write(self, data):
data, bytesdecoded = self.decode(data, self.errors)
return self.writer.write(data)
def writelines(self, list):
data = ''.join(list)
data, bytesdecoded = self.decode(data, self.errors)
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)
### Shortcuts
def open(filename, mode='rb', 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.
Files are always opened in binary mode, even if no binary mode
was specified. This is done to avoid data loss due to encodings
using 8-bit values. The default file mode is 'rb' meaning to
open the file in binary 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.
"""
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)
srw = StreamReaderWriter(file, sr, sw, errors)
# Add attributes to simplify introspection
srw.encoding = encoding
return srw
def EncodedFile(file, data_encoding, file_encoding=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 data_encoding and then written to the original
file as string using file_encoding. The intermediate encoding
will usually be Unicode but depends on the specified codecs.
Strings are read from the file using file_encoding and then
passed back to the caller as string 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.
"""
if file_encoding is None:
file_encoding = data_encoding
encode, decode = lookup(data_encoding)[:2]
Reader, Writer = lookup(file_encoding)[2:]
sr = StreamRecoder(file,
encode, decode, Reader, Writer,
errors)
# Add attributes to simplify introspection
sr.data_encoding = data_encoding
sr.file_encoding = file_encoding
return sr
### Helpers for codec lookup
def getencoder(encoding):
""" Lookup up the codec for the given encoding and return
its encoder function.
Raises a LookupError in case the encoding cannot be found.
"""
return lookup(encoding)[0]
def getdecoder(encoding):
""" Lookup up the codec for the given encoding and return
its decoder function.
Raises a LookupError in case the encoding cannot be found.
"""
return lookup(encoding)[1]
def getreader(encoding):
""" Lookup up the codec for the given encoding and return
its StreamReader class or factory function.
Raises a LookupError in case the encoding cannot be found.
"""
return lookup(encoding)[2]
def getwriter(encoding):
""" Lookup up the codec for the given encoding and return
its StreamWriter class or factory function.
Raises a LookupError in case the encoding cannot be found.
"""
return lookup(encoding)[3]
### Helpers for charmap-based codecs
def make_identity_dict(rng):
""" make_identity_dict(rng) -> dict
Return a dictionary where elements of the rng sequence are
mapped to themselves.
"""
res = {}
for i in rng:
res[i]=i
return res
def make_encoding_map(decoding_map):
""" Creates an encoding map from a decoding map.
If a target mapping in the decoding map occurs multiple
times, then that target is mapped to None (undefined mapping),
causing an exception when encountered by the charmap codec
during translation.
One example where this happens is cp875.py which decodes
multiple character to \u001a.
"""
m = {}
for k,v in decoding_map.items():
if not v in m:
m[v] = k
else:
m[v] = None
return m
### error handlers
strict_errors = lookup_error("strict")
ignore_errors = lookup_error("ignore")
replace_errors = lookup_error("replace")
xmlcharrefreplace_errors = lookup_error("xmlcharrefreplace")
backslashreplace_errors = lookup_error("backslashreplace")
# Tell modulefinder that using codecs probably needs the encodings
# package
_false = 0
if _false:
import encodings
### Tests
if __name__ == '__main__':
# Make stdout translate Latin-1 output into UTF-8 output
sys.stdout = EncodedFile(sys.stdout, 'latin-1', 'utf-8')
# Have stdin translate Latin-1 input into UTF-8 input
sys.stdin = EncodedFile(sys.stdin, 'utf-8', 'latin-1')
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