Find intersection

intersect.py

def intersection(sets):
    counts = {}
    for s in sets:
        print "Starting set"
        if not counts:
            for item in s:
                counts[item] = 1
            continue
        changed = False
        for item in s:
            if item in counts:
                changed = True
                counts[item] += 1
        if not changed:
            return set()
    for key in counts.copy():
        if counts[key] is not len(sets):
            del counts[key]
    return counts.keys()