code: def get_common_elements(list1, list2):
      
      #result = []
      #for item in list1:
      #    if item in list2:
      #        result.append(item)
      #Return list(set(list1).intersection(set(list2)))
      set2 = set(list2)
      result = [item for item in list1 if item in set2]
      return result
docs: find the common elements in two lists.  used to support auto align
          might be faster with sets
  
      Parameters
      ----------
      list1 : list
          a list of objects
      list2 : list
          a list of objects
  
      Returns
      -------
      list : list
          list of common objects shared by list1 and list2