queuearray.py

from exceptions import Empty
class ArrayQueue:
    def __init__(self):
        self._data =[]
        self._size =0
        self._front=0
    def __len__(self):
        return self._size
    def is_empty(self):
        return self._size==0
    def enqueue(self,e):
        self._data.append(e)
        self._size=self._size+1
    def dequeue(self):
        if self.is_empty():
            raise Empty('Queue is Empty')
        value = self._data[self._front]
        self._data[self._front] = None
        self._front = self._front + 1
        self._size = self._size - 1
        return value
    def first(self):
        if self.is_empty():
            raise Empty('Queue is Empty')
        return self._data[self._front]

q=ArrayQueue()
q.enqueue(10)
q.enqueue(20)
print('Queue:', q._data)
print('Length: ', len(q))
print('Dequeue: ',q.dequeue())
print('Queue:', q._data)
q.enqueue(30)
q.enqueue(40)
print('Queue:', q._data)
print('First Element: ', q.first())
print('Queue:', q._data)
print('Dequeue: ',q.dequeue())
print('Queue:', q._data)