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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 public_key_to_connection_id(self, public_key):
 """ Get stored connection id for a public key. """

        with self._connections_lock:
            for connection_id, connection_info in self._connections.items():
                if connection_info.public_key == public_key:
                    return connection_id

            return None