queues listing continued self _qhead self _qhead next self _count - return node item private storage class for creating the linked list nodes class _queuenodeobject )def __init__selfitem )self item item self next none priority queues some applications require the use of queue in which items are assigned priority and the items with higher priority are dequeued first howeverall items with the same priority still obey the fifo principle that isif two items with the same priority are enqueuedthe first in will be the first out the priority queue adt priority queue is simply an extended version of the basic queue with the exception that priority must be assigned to each item at the time it is enqueued there are two basic types of priority queuesbounded and unbounded the bounded priority queue assumes small limited range of priorities over the interval of integers [ pthe unbounded priority queue places no limit on the range of integer values that can be used as priorities the definition of the priority queue adt is provided below note that we use one definition for both bounded and unbounded priority queues define priority queue adt priority queue is queue in which each item is assigned priority and items with higher priority are removed before those with lower priorityirrespective of when they were added integer values are used for the priorities with smaller integer value having higher priority bounded priority queue restricts the priorities to the integer values between zero and predefined upper limit whereas an unbounded priority queue places no limits on the range of priorities priorityqueue()creates new empty unbounded priority queue bpriorityqueuenumlevels )creates new empty bounded priority queue with priority levels in the range from to numlevels isempty()returns boolean value indicating whether the queue is empty