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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 set_tunnel(self, host, port=None, headers=None):
 """ Sets up the host and the port for the HTTP CONNECT Tunnelling. The headers argument should be a mapping of extra HTTP headers to send with the CONNECT request. """

        self._tunnel_host = host
        self._tunnel_port = port
        if headers:
            self._tunnel_headers = headers
        else:
            self._tunnel_headers.clear()