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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 start(self):
 """ Start executor with additional checks. Checks if previous executor isn't running then start process (executor) and wait until it's started. :returns: itself :rtype: Executor """

        if self.pre_start_check():
            # Some other executor (or process) is running with same config:
            raise AlreadyRunning(self)

        super(Executor, self).start()

        self.wait_for(self.check_subprocess)
        return self