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The other exceptions occur when strings or unicode objects 
are passed in as an argument.  The string that it fails on is 
the empty string ('').  I can see disallowing non-ascii names, 
but '' should raise a LookupError.

My use case is to see if an user supplied unicode string is a 
valid encoding, so any check that the lookup function does 
not do, I will need to do before calling it.