class_docstr: An OrderedSet is a custom MutableSet that remembers its order, so that
  every entry has an index that can be looked up.
  
  Example:
      >>> OrderedSet([1, 1, 2, 3, 2])
      OrderedSet([1, 2, 3])
class_docstr_tok: ["An","OrderedSet","is","a","custom","MutableSet","that","remembers","its","order",",","so","that","every","entry","has","an","index","that","can","be","looked","up",".","Example",":",">",">",">","OrderedSet","(","[","1",",","1",",","2",",","3",",","2","]",")","OrderedSet","(","[","1",",","2",",","3","]",")"]
docstr: Combines all unique items.
  Each items order is defined by its first appearance.
  
  Example:
      >>> oset = OrderedSet.union(OrderedSet([3, 1, 4, 1, 5]), [1, 3], [2, 0])
      >>> print(oset)
      OrderedSet([3, 1, 4, 5, 2, 0])
      >>> oset.union([8, 9])
      OrderedSet([3, 1, 4, 5, 2, 0, 8, 9])
      >>> oset | {10}
      OrderedSet([3, 1, 4, 5, 2, 0, 10])
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code: def union(self, *sets):
      """
      Combines all unique items.
      Each items order is defined by its first appearance.
  
      Example:
          >>> oset = OrderedSet.union(OrderedSet([3, 1, 4, 1, 5]), [1, 3], [2, 0])
          >>> print(oset)
          OrderedSet([3, 1, 4, 5, 2, 0])
          >>> oset.union([8, 9])
          OrderedSet([3, 1, 4, 5, 2, 0, 8, 9])
          >>> oset | {10}
          OrderedSet([3, 1, 4, 5, 2, 0, 10])
      """
      cls = (
          self.__class__ if isinstance(self, OrderedSet) else OrderedSet
      )
      containers = map(list, it.chain([self], sets))
      items = it.chain.from_iterable(containers)
      return cls(items)
  
imports: import itertools
  from collections import deque
label_desc: Use image node_id 18 for calling the OrderedSet obj's underlying member method code with example usage: obj.union() and returns: cls