""" 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() -> codecs.CodecInfo object
The getregentry() API must return a CodecInfo object with encoder, decoder,
incrementalencoder, incrementaldecoder, streamwriter and streamreader
atttributes 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 ([email protected]).

(c) Copyright CNRI, All Rights Reserved. NO WARRANTY.

"""#"

import codecs
from . import aliases

_cache = {}
_unknown = '--unknown--'
_import_tail = ['*']
_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.

"""
if isinstance(encoding, bytes):
encoding = str(encoding, "ascii")
chars = []
punct = False
for c in encoding:
if c.isalnum() or c == '.':
if punct and chars:
chars.append('_')
chars.append(c)
punct = False
else:
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,
norm_encoding]
else:
modnames = [norm_encoding]
for modname in modnames:
if not modname or '.' in modname:
continue
try:
# 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,
level=0)
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 = 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)
try:
codecaliases = mod.getaliases()
except AttributeError:
pass
else:
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
codecs.register(search_function)