code: def push(self, item, priority=None):
          
          priority = item if priority is None else priority
          node = PriorityQueueNode(item, priority)
          for index, current in enumerate(self.priority_queue_list):
              if current.priority < node.priority:
                  self.priority_queue_list.insert(index, node)
                  return
          # when traversed complete queue
          self.priority_queue_list.append(node)
docs: Push the item in the priority queue.
          if priority is not given, priority is set to the value of item.