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""" Standard "encodings" Package
Standard Python encoding modules are stored in this package
directory.
Codec modules must have names corresponding to normalized encoding
names as defined in the normalize_encoding() function below, e.g.
'utf-8' must be implemented by the module 'utf_8.py'.
Each codec module must export the following interface:
* getregentry() -> (encoder, decoder, stream_reader, stream_writer)
The getregentry() API must return callable objects which adhere to
the Python Codec Interface Standard.
In addition, a module may optionally also define the following
APIs which are then used by the package's codec search function:
* getaliases() -> sequence of encoding name strings to use as aliases
Alias names returned by getaliases() must be normalized encoding
names as defined by normalize_encoding().
Written by Marc-Andre Lemburg (mal@lemburg.com).
(c) Copyright CNRI, All Rights Reserved. NO WARRANTY.
"""#"
import codecs, types
from . import aliases
_cache = {}
_unknown = '--unknown--'
_import_tail = ['*']
_norm_encoding_map = (' . '
'0123456789 ABCDEFGHIJKLMNOPQRSTUVWXYZ '
' abcdefghijklmnopqrstuvwxyz '
' '
' '
' ')
_aliases = aliases.aliases
class CodecRegistryError(LookupError, SystemError):
pass
def normalize_encoding(encoding):
""" Normalize an encoding name.
Normalization works as follows: all non-alphanumeric
characters except the dot used for Python package names are
collapsed and replaced with a single underscore, e.g. ' -;#'
becomes '_'. Leading and trailing underscores are removed.
Note that encoding names should be ASCII only; if they do use
non-ASCII characters, these must be Latin-1 compatible.
"""
# Make sure we have an 8-bit string, because .translate() works
# differently for Unicode strings.
if type(encoding) is types.UnicodeType:
# Note that .encode('latin-1') does *not* use the codec
# registry, so this call doesn't recurse. (See unicodeobject.c
# PyUnicode_AsEncodedString() for details)
encoding = encoding.encode('latin-1')
return '_'.join(encoding.translate(_norm_encoding_map).split())
def search_function(encoding):
# Cache lookup
entry = _cache.get(encoding, _unknown)
if entry is not _unknown:
return entry
# Import the module:
#
# First try to find an alias for the normalized encoding
# name and lookup the module using the aliased name, then try to
# lookup the module using the standard import scheme, i.e. first
# try in the encodings package, then at top-level.
#
norm_encoding = normalize_encoding(encoding)
aliased_encoding = _aliases.get(norm_encoding) or \
_aliases.get(norm_encoding.replace('.', '_'))
if aliased_encoding is not None:
modnames = [aliased_encoding,
norm_encoding]
else:
modnames = [norm_encoding]
for modname in modnames:
if not modname:
continue
try:
mod = __import__('encodings.' + modname,
globals(), locals(), _import_tail)
except ImportError:
pass
else:
break
else:
mod = None
try:
getregentry = mod.getregentry
except AttributeError:
# Not a codec module
mod = None
if mod is None:
# Cache misses
_cache[encoding] = None
return None
# Now ask the module for the registry entry
entry = tuple(getregentry())
if len(entry) != 4:
raise CodecRegistryError,\
'module "%s" (%s) failed to register' % \
(mod.__name__, mod.__file__)
for obj in entry:
if not callable(obj):
raise CodecRegistryError,\
'incompatible codecs in module "%s" (%s)' % \
(mod.__name__, mod.__file__)
# Cache the codec registry entry
_cache[encoding] = entry
# Register its aliases (without overwriting previously registered
# aliases)
try:
codecaliases = mod.getaliases()
except AttributeError:
pass
else:
for alias in codecaliases:
if not _aliases.has_key(alias):
_aliases[alias] = modname
# Return the registry entry
return entry
# Register the search_function in the Python codec registry
codecs.register(search_function)
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