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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 _reset_server(self, address):
 """Clear our pool for a server and mark it Unknown. Hold the lock when calling this. Does *not* request an immediate check. """

        server = self._servers.get(address)

        # "server" is None if another thread removed it from the topology.
        if server:
            server.reset()

            # Mark this server Unknown.
            self._description = self._description.reset_server(address)
            self._update_servers()