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123 lines
3.6 KiB
Python
123 lines
3.6 KiB
Python
""" Standard "encodings" Package
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Standard Python encoding modules are stored in this package
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directory.
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Codec modules must have names corresponding to normalized encoding
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names as defined in the normalize_encoding() function below, e.g.
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'utf-8' must be implemented by the module 'utf_8.py'.
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Each codec module must export the following interface:
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* getregentry() -> (encoder, decoder, stream_reader, stream_writer)
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The getregentry() API must return callable objects which adhere to
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the Python Codec Interface Standard.
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In addition, a module may optionally also define the following
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APIs which are then used by the package's codec search function:
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* getaliases() -> sequence of encoding name strings to use as aliases
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Alias names returned by getaliases() must be normalized encoding
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names as defined by normalize_encoding().
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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 codecs, exceptions, re
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_cache = {}
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_unknown = '--unknown--'
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_import_tail = ['*']
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_norm_encoding_RE = re.compile('[^a-zA-Z0-9.]')
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class CodecRegistryError(exceptions.LookupError,
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exceptions.SystemError):
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pass
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def normalize_encoding(encoding):
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""" Normalize an encoding name.
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Normalization works as follows: all non-alphanumeric
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characters except the dot used for Python package names are
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collapsed and replaced with a single underscore, e.g. ' -;#'
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becomes '_'.
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"""
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return '_'.join(_norm_encoding_RE.split(encoding))
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def search_function(encoding):
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# Cache lookup
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entry = _cache.get(encoding, _unknown)
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if entry is not _unknown:
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return entry
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# Import the module:
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#
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# First look in the encodings package, then try to lookup the
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# encoding in the aliases mapping and retry the import using the
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# default import module lookup scheme with the alias name.
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#
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modname = normalize_encoding(encoding)
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try:
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mod = __import__('encodings.' + modname,
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globals(), locals(), _import_tail)
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except ImportError:
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import aliases
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modname = (aliases.aliases.get(modname) or
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aliases.aliases.get(modname.replace('.', '_')) or
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modname)
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try:
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mod = __import__(modname, globals(), locals(), _import_tail)
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except ImportError:
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mod = None
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try:
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getregentry = mod.getregentry
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except AttributeError:
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# Not a codec module
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mod = None
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if mod is None:
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# Cache misses
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_cache[encoding] = None
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return None
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# Now ask the module for the registry entry
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entry = tuple(getregentry())
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if len(entry) != 4:
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raise CodecRegistryError,\
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'module "%s" (%s) failed to register' % \
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(mod.__name__, mod.__file__)
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for obj in entry:
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if not callable(obj):
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raise CodecRegistryError,\
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'incompatible codecs in module "%s" (%s)' % \
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(mod.__name__, mod.__file__)
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# Cache the codec registry entry
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_cache[encoding] = entry
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# Register its aliases (without overwriting previously registered
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# aliases)
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try:
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codecaliases = mod.getaliases()
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except AttributeError:
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pass
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else:
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import aliases
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for alias in codecaliases:
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if not aliases.aliases.has_key(alias):
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aliases.aliases[alias] = modname
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# Return the registry entry
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return entry
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# Register the search_function in the Python codec registry
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codecs.register(search_function)
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