Python program to implement Queue Operations

queue: implemented as a list

front: integer having position of first (frontmost) element in queue

rear: integer having position of last element in queue

def cls():
    print("\n"*100)
def isEmpty(qu):
    if qu==[]:
        return True
    else:
        return False
def Enqueue(qu,item):
    qu.append(item)
    if len(qu)==1:
        front=rear=0
    else:
        rear=len(qu)-1
def Dequeue(qu):
    if isEmpty(qu):
        return "Underflow"
    else:
        item=qu.pop(0)
    if len(qu)==0:
        front=rear=None
    return item
def Peek(qu):
    if isEmpty(qu):
        return "Underflow"
    else:
        front=0
    return qu[front]
def Display(qu):
    if isEmpty(qu):
        print("Queue Empty!")
    elif len(qu)==1:
        print(qu[0],"<== front,rear")
    else:
        front=0
        rear=len(qu)-1
        print(qu[front],"<==front")
        for a in  range(1,rear):
            print(qu[a])
        print(qu[rear],"<--rear")


#__main__

queue=[]
front=None
while True:
    cls()
    print("Queue Operations")
    print("1.Enqueue")
    print("2.Dequeue")
    print("3.Peek")
    print("4.Display Queue")
    print("5.Exit")
    ch=int(input("Enter your choice(1-5):"))
    if ch==1:
        item=int(input("Enter item:"))
        Enqueue(queue,item)
        input("Press Enter to continue...")
    elif ch==2:
        item=Dequeue(queue)
        if item=="Underflow":
            print("Underflow!Queue is Empty")
        else:
            print("Dequeue-ed item is",item)
        input("Press Enter to continue...")
    elif ch==3:
        item=Peek(queue)
        if item=="Underflow":
            print("Queue is empty!")
        else:
            print("Frontmost item is",item)
        input("Press Enter to continue...")
    elif ch==4:
        Display(queue)
        input("Press Enter to continue...")
    elif ch==5:
        break
    else:
        print("Invalid choice!")
        input("Press Enter to continue...")

Output:

Queue Operations
1.Enqueue
2.Dequeue
3.Peek
4.Display Queue
5.Exit
Enter your choice(1-5):1
Enter item:15
Press Enter to continue…

Queue Operations
1.Enqueue
2.Dequeue
3.Peek
4.Display Queue
5.Exit
Enter your choice(1-5):1
Enter item:35
Press Enter to continue…

Queue Operations
1.Enqueue
2.Dequeue
3.Peek
4.Display Queue
5.Exit
Enter your choice(1-5):1
Enter item:45
Press Enter to continue…

Queue Operations
1.Enqueue
2.Dequeue
3.Peek
4.Display Queue
5.Exit
Enter your choice(1-5):2
Dequeue-ed item is 15
Press Enter to continue…

Queue Operations
1.Enqueue
2.Dequeue
3.Peek
4.Display Queue
5.Exit
Enter your choice(1-5):3
Frontmost item is 35
Press Enter to continue…

Queue Operations
1.Enqueue
2.Dequeue
3.Peek
4.Display Queue
5.Exit
Enter your choice(1-5):4
35 <==front
45 <–rear
Press Enter to continue…

Queue Operations
1.Enqueue
2.Dequeue
3.Peek
4.Display Queue
5.Exit
Enter your choice(1-5):5