Implementing a Queue in Python

The program creates a queue and allows the user to perform enqueue and dequeue operations on it.

It is again appropriate to create a new class for the implementation of the abstract data type queue. As before, we will use the power and simplicity of the list collection to build the internal representation of the queue.

We need to decide which end of the list to use as the rear and which to use as the front. The implementation shown in Listing 1 assumes that the rear is at position 0 in the list. This allows us to use the insert function on lists to add new elements to the rear of the queue. The pop operation can be used to remove the front element (the last element of the list). Recall that this also means that enqueue will be O(n) and dequeue will be O(1).

class Queue:
    def __init__(self):
        self.__items = []

    def is_empty(self):
        return self.__items == []

    def enqueue(self, item):
        self.__items.insert(0, item)

    def dequeue(self):
        return self.__items.pop()

    def size(self):
        return len(self.__items)


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