queue.py

class Queue:
    def __init__(self):
        self.items = []
        self.frontIdx = 0
        
    def __compress(self):
        newitems = []
        for i in range(self.frontIdx,len(self.items)):
            newitems.append(self.items[i])
            
        self.items = newitems
        self.frontIdx = 0
        
    def dequeue(self):
        if self.isEmpty():
            raise RuntimeError("Attempt to dequeue an empty queue")
        
        # When queue is half full, compress it. This 
        # achieves an amortized complexity of O(1) while
        # not letting the list continue to grow unchecked. 
        if self.frontIdx * 2 > len(self.items):
            self.__compress()
            
        item = self.items[self.frontIdx]
        self.frontIdx += 1
        return item
    
    def enqueue(self,item):
        self.items.append(item)
        
    def front(self):
        if self.isEmpty():
            raise RuntimeError("Attempt to access front of empty queue")
        
        return self.items[self.frontIdx]
        
    
    def isEmpty(self):
        return self.frontIdx == len(self.items)

    def clear(self):
        self.items = []
        self.frontIdx = 0
    
def main():
    q = Queue()
    items = list(range(10))
    items2 = []
    
    for k in items:
        q.enqueue(k)
        
    if q.front() == 0:
        print("Test 1 Passed")
    else:
        print("Test 1 Failed")
        
    while not q.isEmpty():
        items2.append(q.dequeue())
    
    if items2 != items:
        print("Test 2 Failed")
    else:
        print("Test 2 Passed")

    for k in items:
        q.enqueue(k)   
      
    items2 = []
    
    while not q.isEmpty():
        items2.append(q.dequeue())  
        
    if items2 != items:
        print("Test 3 Failed")
    else:
        print("Test 3 Passed")
    
    try:
        q.dequeue()
        print("Test 4 Failed")
        
    except RuntimeError:
        print("Test 4 Passed")
    except:
        print("Test 4 Failed")

    try:
        q.front()
        print("Test 5 Failed")
        
    except RuntimeError:
        print("Test 5 Passed")
    except:
        print("Test 5 Failed")  
        
if __name__=="__main__":
    main()