152 lines
4.9 KiB
Python
152 lines
4.9 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() -> codecs.CodecInfo object
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The getregentry() API must return a CodecInfo object with encoder, decoder,
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incrementalencoder, incrementaldecoder, streamwriter and streamreader
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atttributes which adhere to 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
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from . import aliases
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_cache = {}
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_unknown = '--unknown--'
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_import_tail = ['*']
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_aliases = aliases.aliases
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class CodecRegistryError(LookupError, 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 '_'. Leading and trailing underscores are removed.
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Note that encoding names should be ASCII only; if they do use
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non-ASCII characters, these must be Latin-1 compatible.
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"""
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if isinstance(encoding, bytes):
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encoding = str(encoding, "ascii")
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chars = []
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punct = False
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for c in encoding:
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if c.isalnum() or c == '.':
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if punct and chars:
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chars.append('_')
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chars.append(c)
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punct = False
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else:
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punct = True
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return ''.join(chars)
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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 try to find an alias for the normalized encoding
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# name and lookup the module using the aliased name, then try to
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# lookup the module using the standard import scheme, i.e. first
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# try in the encodings package, then at top-level.
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#
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norm_encoding = normalize_encoding(encoding)
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aliased_encoding = _aliases.get(norm_encoding) or \
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_aliases.get(norm_encoding.replace('.', '_'))
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if aliased_encoding is not None:
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modnames = [aliased_encoding,
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norm_encoding]
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else:
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modnames = [norm_encoding]
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for modname in modnames:
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if not modname or '.' in modname:
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continue
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try:
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# Import is absolute to prevent the possibly malicious import of a
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# module with side-effects that is not in the 'encodings' package.
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mod = __import__('encodings.' + modname, fromlist=_import_tail,
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level=0)
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except ImportError:
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pass
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else:
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break
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else:
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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 = getregentry()
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if not isinstance(entry, codecs.CodecInfo):
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if not 4 <= len(entry) <= 7:
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raise CodecRegistryError('module "%s" (%s) failed to register'
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% (mod.__name__, mod.__file__))
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if not callable(entry[0]) or not callable(entry[1]) or \
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(entry[2] is not None and not callable(entry[2])) or \
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(entry[3] is not None and not callable(entry[3])) or \
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(len(entry) > 4 and entry[4] is not None and not callable(entry[4])) or \
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(len(entry) > 5 and entry[5] is not None and not callable(entry[5])):
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raise CodecRegistryError('incompatible codecs in module "%s" (%s)'
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% (mod.__name__, mod.__file__))
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if len(entry)<7 or entry[6] is None:
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entry += (None,)*(6-len(entry)) + (mod.__name__.split(".", 1)[1],)
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entry = codecs.CodecInfo(*entry)
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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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for alias in codecaliases:
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if alias not in _aliases:
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_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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