dic1 = {"a": "AAA", "b": "BBB", "c": "CCC", "f": "FFF" }
dic2 = {"b": "BBB", "d": "DDD", "e": "EEE" }
keysunion = sorted(list(set(dic1.keys() + dic2.keys())))
print keysunion # -> ['a', 'b', 'c', 'd', 'e', 'f']
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