[Tutor] filtering within a function.

[Tesla Coil]

Revising cipher.py...
http://www.lowerstandard.com/python/cipher.py
to eliminate import of string, and discovered
that the unstray function is bugged something
awful (guess it usually gets the right input;
this has gone unnoticed for a couple months).

Given:
>>> foo = list('UPPERlowerUPPER12345')

This appears to work:

>>> uppercase = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
>>> def f(x): return x in uppercase
... 
>>> filter(f, foo)
['U', 'P', 'P', 'E', 'R', 'U', 'P', 'P', 'E', 'R']

Can't seem to make it work inside the function.