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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 change_port_speed(self, instance_id, public, speed):
 """Allows you to change the port speed of a virtual server's NICs. Example:: #change the Public interface to 10Mbps on instance 12345 result = mgr.change_port_speed(instance_id=12345, public=True, speed=10) # result will be True or an Exception :param int instance_id: The ID of the VS :param bool public: Flag to indicate which interface to change. True (default) means the public interface. False indicates the private interface. :param int speed: The port speed to set. .. warning:: A port speed of 0 will disable the interface. """

        if public:
            return self.client.call('Virtual_Guest', 'setPublicNetworkInterfaceSpeed',
                                    speed, id=instance_id)
        else:
            return self.client.call('Virtual_Guest', 'setPrivateNetworkInterfaceSpeed',
                                    speed, id=instance_id)