def _ListUnion(list_1, list_2):
 if (not (isinstance(list_1, list) and isinstance(list_2, list))):
  raise TypeError('Arguments must be lists.')
 union = []
 for x in (list_1 + list_2):
  if (x not in union):
   union.append(x)
 return union

def _ListUnion ( list_1 , list_2 ) : if ( not ( isinstance ( list_1 , list ) and isinstance ( list_2 , list ) ) ) : raise TypeError ( 'Arguments must be lists.' ) union = [ ] for x in ( list_1 + list_2 ) : if ( x not in union ) : union . append ( x ) return union
returns the union of two lists .