code: def _compare_keys(element1, element2, key, compare_func, *args):
      
      if key in element1 and key in element2:
          if not compare_func(element1[key], element2[key], *args):
              return False
      elif key in element1 or key in element2:
          return False
  
      return True
docs: Compares a specific key between two elements of a basis set
  
      If the key exists in one element but not the other, False is returned.
  
      If the key exists in neither element, True is returned.
  
      Parameters
      ----------
      element1 : dict
          Basis info for an element
      element2 : dict
          Basis info for another element
      key : string
          Key to compare in the two elements
      compare_func : function
          Function that returns True if the data under the key is equivalent
          in both elements
      args
          Additional arguments to be passed to compare_Func