def opt_port(self, portstr):
        """
        Specify the port number to listen on.
        """
        try:
            self['port'] = int(portstr)
        except __HOLE__:
            raise UsageError(
                "Specify an integer between 0 and 65535 as a port number.")
        if self['port'] >= 2 ** 16:
            raise UsageError(
                "Specify an integer between 0 and 65535 as a port number.")
        elif self['port'] < 0:
            raise UsageError(
                "Specify an integer between 0 and 65535 as a port number.")
dataset/ETHPy150Open twisted/nevow/nevow/_widget_plugin.py/Options.opt_port