code: def deregister(self, key):
          
  
          if not key in self._actions:
              return False
  
          del self._actions[key]
  
          if key in self._cache:
              del self._cache[key]
  
          return True
docs: Deregisters an existing key.
  
              `key`
                  String key to deregister.
  
              Returns boolean.