[x.lower() for x in ["A","B","C"]] ['a', 'b', 'c'] >>> [x.upper() for x in ["a","b","c"]] ['A', 'B', 'C'] >>> map(lambda x:x.lower(),["A","B","C"]) ['a', 'b', 'c'] >>> map(lambda x:x.upper(),["a","b","c"]) ['A', 'B', 'C']