'twostack get('onestack empty(true stack get(timeout= traceback (most recent call last)file ""line in stack get(timeout= file "/usr/lib /python /queue py"line in get raise empty queue empty you might wonder why you couldn' just use the append(and pop(methods on standard list quite franklythat' probably what would do rarely have occasion to use the lifoqueue class in production code working with the end of list is an efficient operationso efficientin factthat the lifoqueue uses standard list under the hoodthere are couple of reasons that you might want to use lifoqueue instead of list the most important one is that lifoqueue supports clean concurrent access from multiple threads if you need stack-like behavior in concurrent settingyou should leave the list at home secondlifoqueue enforces the stack interface you can' unwittingly insert value to the wrong position in lifoqueuefor example (althoughas an exerciseyou can work out how to do this completely wittinglypriority queues the priority queue enforces very different style of ordering from the previous queue implementations once againthey follow the exact same get(and put(apibut instead of relying on the order that items arrive to determine when they should be returnedthe most "importantitem is returned by conventionthe most importantor highest priority item is the one that sorts lowest using the less than operator common convention is to store tuples in the priority queuewhere the first element in the tuple is the priority for that elementand the second element is the data another common paradigm is to implement the __lt__ methodas we discussed earlier in this it is perfectly acceptable to have multiple elements with the same priority in the queuealthough there are no guarantees on which one will be returned first