def rankings(filename,school):
    d = {}
    f = open(filename)
    for line in f:
        parts = line.split(":")
        prof = parts[1]
        dept = parts[2]
        rank = float(parts[3])
        if parts[0] == school:
            key = (prof,dept)
            if key not in d:
                d[key] = []
            d[key].append(rank)
    
    # (name,school) : [1,2,3,4]
    
    for key in d:
        d[key] = sum(d[key])/len(d[key])
    
    # now sort the tuples (name,dept,ranking)
    # first create the tuples, then sort them
    
    tups = [(t[0],t[1],d[t]) for t in d]
    tups = sorted(tups) # alphabetical by name
    return sorted(tups, key=operator.itemgetter(2),reverse=True)