Skip to content
Branch: master
Find file Copy path
Find file Copy path
14 contributors

Users who have contributed to this file

@malemburg @gvanrossum @zooba @loewis @tim-one @Yhg1s @nnorwitz @brettcannon @vstinner @tirkarthi @florentx @collinw @warsaw @asottile
170 lines (138 sloc) 5.46 KB
""" Standard "encodings" Package
Standard Python encoding modules are stored in this package
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 ''.
Each codec module must export the following interface:
* getregentry() -> codecs.CodecInfo object
The getregentry() API must return a CodecInfo object with encoder, decoder,
incrementalencoder, incrementaldecoder, streamwriter and streamreader
attributes 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 (
(c) Copyright CNRI, All Rights Reserved. NO WARRANTY.
import codecs
import sys
from . import aliases
_cache = {}
_unknown = '--unknown--'
_import_tail = ['*']
_aliases = aliases.aliases
class CodecRegistryError(LookupError, SystemError):
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 isinstance(encoding, bytes):
encoding = str(encoding, "ascii")
chars = []
punct = False
for c in encoding:
if c.isalnum() or c == '.':
if punct and chars:
punct = False
punct = True
return ''.join(chars)
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,
modnames = [norm_encoding]
for modname in modnames:
if not modname or '.' in modname:
# Import is absolute to prevent the possibly malicious import of a
# module with side-effects that is not in the 'encodings' package.
mod = __import__('encodings.' + modname, fromlist=_import_tail,
except ImportError:
# ImportError may occur because 'encodings.(modname)' does not exist,
# or because it imports a name that does not exist (see mbcs and oem)
mod = None
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 = getregentry()
if not isinstance(entry, codecs.CodecInfo):
if not 4 <= len(entry) <= 7:
raise CodecRegistryError('module "%s" (%s) failed to register'
% (mod.__name__, mod.__file__))
if not callable(entry[0]) or not callable(entry[1]) or \
(entry[2] is not None and not callable(entry[2])) or \
(entry[3] is not None and not callable(entry[3])) or \
(len(entry) > 4 and entry[4] is not None and not callable(entry[4])) or \
(len(entry) > 5 and entry[5] is not None and not callable(entry[5])):
raise CodecRegistryError('incompatible codecs in module "%s" (%s)'
% (mod.__name__, mod.__file__))
if len(entry)<7 or entry[6] is None:
entry += (None,)*(6-len(entry)) + (mod.__name__.split(".", 1)[1],)
entry = codecs.CodecInfo(*entry)
# Cache the codec registry entry
_cache[encoding] = entry
# Register its aliases (without overwriting previously registered
# aliases)
codecaliases = mod.getaliases()
except AttributeError:
for alias in codecaliases:
if alias not in _aliases:
_aliases[alias] = modname
# Return the registry entry
return entry
# Register the search_function in the Python codec registry
if sys.platform == 'win32':
def _alias_mbcs(encoding):
import _winapi
ansi_code_page = "cp%s" % _winapi.GetACP()
if encoding == ansi_code_page:
import encodings.mbcs
return encodings.mbcs.getregentry()
except ImportError:
# Imports may fail while we are shutting down
You can’t perform that action at this time.