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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 request(self, method, args, response_cb):
 """Send a msgpack-rpc request to Nvim. A msgpack-rpc with method `method` and argument `args` is sent to Nvim. The `response_cb` function is called with when the response is available. """

        request_id = self._next_request_id
        self._next_request_id = request_id + 1
        self._msgpack_stream.send([0, request_id, method, args])
        self._pending_requests[request_id] = response_cb