code: def union(*argv):
          
          res = OrderedSet()
          for ods in argv:
              res = res | ods
          return res
docs: Returns union of sets as a new set. basically it's
          Items are ordered by set1, set2, ...
          
          **中文文档**
          
          求多个有序集合的并集, 按照第一个集合, 第二个, ..., 这样的顺序。