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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 get_instance_attribute(self, instance_id, attribute):
 """ Gets an attribute from an instance. :type instance_id: string :param instance_id: The Amazon id of the instance :type attribute: string :param attribute: The attribute you need information about Valid choices are: * instanceType|kernel|ramdisk|userData| * disableApiTermination| * instanceInitiatedShutdownBehavior| * rootDeviceName|blockDeviceMapping :rtype: :class:`boto.ec2.image.InstanceAttribute` :return: An InstanceAttribute object representing the value of the attribute requested """

        params = {'InstanceId' : instance_id}
        if attribute:
            params['Attribute'] = attribute
        return self.get_object('DescribeInstanceAttribute', params,
                               InstanceAttribute, verb='POST')