<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get(self, key):
 """ Executes the callable registered at the specified key and returns its value. Subsequent queries are cached internally. `key` String key for a previously stored callable. """


        if not key in self._actions:
            return None
        if not key in self._cache:
            self._cache[key] = self._actions[key]()

        return self._cache[key]