code: def load_parent_implems(self, parent_implems):
          
          for trname, attr, implem in parent_implems.get_custom_implementations():
              self.implementations[trname] = implem.copy()
              self.transitions_at[trname] = attr
              self.custom_implems.add(trname)
docs: Import previously defined implementations.
  
          Args:
              parent_implems (ImplementationList): List of implementations defined
                  in a parent class.