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The point of using a function is to allow the function special hanling of the encoding name, which goes beyond a simple map lookup, i.e. you could do the following:
 import codecs
 def search_function(encoding):
 if not encoding.startswith("append-"):
 return None
 suffix = encoding[7:]
 def encode(s, errors="strict"):
 s = (s + suffix).encode("utf-8", errors)
 return (s, len(s))
 def decode(s, errors="strict"):
 s = bytes(s).decode("utf-8", errors)
 if s.endswith(suffix):
 s = s[:-len(suffix)]
 return (s, len(s))
 return codecs.CodecInfo(encode, decode, name=encoding)
 codecs.register(search_function)
 $ python
 Python 3.3.1 (default, Apr 29 2013, 15:35:47)
 [GCC 4.2.1 Compatible Apple LLVM 4.2 (clang-425.0.24)] on darwin
 Type "help", "copyright", "credits" or "license" for more information.
 >>> import appendcodec
 >>> 'foo'.encode('append-bar')
 b'foobar'
 >>> b'foobar'.decode('append-bar')
 'foo'
The search function can't return a list of codec names in this case, as the list is infinite.