Exercise: Subset of a set

The task here is to produce a memory efficient way of representing a subset of a given base set. We will use bytes, and for simplicity we assume that the base set has at most eight elements.

In Python 2.6 bytes is an alternative name for string, and in Python 3 it is a separate type in its own right (with a somewhat different interface). Please do the exercise in Python 2.6 (or earlier, with bytes equal to str).

The interface I suggest is something like

all_vowels = 'aeiou'
SubsetOfVowels = SubsetClassFactory(all_vowels)

my_vowels = SubsetOfVowels('ie')
set(my_vowels) == set(['i', 'e'])
ord(my_vowels[0]) == 2 + 4

Don’t deal with set operations, such as intersection or complement.

By the way, an application would be dealing with large numbers of subsets of a largish set (set 255 elements), using numpy to store the data and do the hard work. So set operation details would have to fit in with numpy.