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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_drive_rotational_speed_rpm(system_obj):
 """Gets the set of rotational speed rpms of the disks. :param system_obj: The HPESystem object. :returns the set of rotational speed rpms of the HDD devices. """

    speed = set()
    smart_resource = _get_attribute_value_of(system_obj, 'smart_storage')
    if smart_resource is not None:
        speed.update(_get_attribute_value_of(
            smart_resource, 'drive_rotational_speed_rpm', default=set()))
    storage_resource = _get_attribute_value_of(system_obj, 'storages')
    if storage_resource is not None:
        speed.update(_get_attribute_value_of(
            storage_resource, 'drive_rotational_speed_rpm', default=set()))
    return speed