Reversing a Dictionary (Alternate)

create_rdict_alt.py

def create_rdict(d):
    """
    Return a dictionary with each value mapping to a set of keys.
    """
    rd = {}
    for (key,value) in d.items():
        if rd.has_key(value):
            rd[value].add(key)
        else:
            rd[value] = set([key])

    return rd