Case-insensitive comparison of sets in Python

Question

I have two sets (although I can do lists, or whatever):

a = frozenset((\'Today\',\'I\',\'am\',\'fine\'))
b = frozenset((\'hello\',\'how\',\'are\',\'you\',\'t         


        

Answer 1

Here's version that works for any pair of iterables:

def intersection(iterableA, iterableB, key=lambda x: x):
    """Return the intersection of two iterables with respect to `key` function.

    """
    def unify(iterable):
        d = {}
        for item in iterable:
            d.setdefault(key(item), []).append(item)
        return d

    A, B = unify(iterableA), unify(iterableB)

    return [(A[k], B[k]) for k in A if k in B]

Example:

print intersection('Today I am fine'.split(),
                   'Hello How a re you TODAY'.split(),
                   key=str.lower)
# -> [(['Today'], ['TODAY'])]