def opt_reactor(self, name):
        """
        The name of the reactor to use.
        (options: {options})
        """
        # Actually actually actually install the reactor right at this very
        # moment, before any other code (for example, a sub-command plugin)
        # runs and accidentally imports and installs the default reactor.
        try:
            self["reactor"] = self.installReactor(name)
        except NoSuchReactor:
            raise UsageError("Unknown reactor: {}".format(name))
        else:
            self["reactorName"] = name

        The name of the reactor to use.
        (options: {options})
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/twist/_options.py