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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_exit_callback(self, callback: Callable[[int], None]) -> None: """Runs ``callback`` when this process exits. The callback takes one argument, the return code of the process. This method uses a ``SIGCHLD`` handler, which is a global setting and may conflict if you have other libraries trying to handle the same signal. If you are using more than one ``IOLoop`` it may be necessary to call `Subprocess.initialize` first to designate one ``IOLoop`` to run the signal handlers. In many cases a close callback on the stdout or stderr streams can be used as an alternative to an exit callback if the signal handler is causing a problem. Availability: Unix """

        self._exit_callback = callback
        Subprocess.initialize()
        Subprocess._waiting[self.pid] = self
        Subprocess._try_cleanup_process(self.pid)