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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def delete(self, key: str) -> None: """ Deletes a setting from this object's storage. The write to the database is performed immediately and the cache in the cache backend is flushed. The cache within this object will be updated correctly. """

        if key in self._write_cache():
            self._write_cache()[key].delete()
            del self._write_cache()[key]

        if key in self._cache():
            del self._cache()[key]

        self._flush_external_cache()