stacks.py

def isEmpty(stk):
    if stk==[]:
        return True
    else:
        return False

def Push(stk,item):
    stk.append(item)
    top=len(stk)-1

def Pop(stk):
    if isEmpty(stk):
        return "Underflow"
    else:
        item=stk.pop()
        if len(stk)==0:
            top=None
        else:
            top=len(stk)-1
        return item

def Peek(stk):
    if isEmpty(stk):
        return "Underflow"
    else:
        top=len(stk)-1
        return stk[top]

def Display(stk):
    if isEmpty(stk):
        print("Stack empty")
    else:
        top=len(stk)-1
        print(stk[top],"<- top")
        for a in range(top-1,-1,-1):
            print(stk[a])

Stack=[]
top=None

while True:
    print("Stack Operations")
    print("1. Push")
    print("2. Pop")
    print("3. Peek")
    print("4. Display stack")
    print("5. Exit")
    ch=int(input("Enter your choice(1-5)"))
    if ch==1:
        item=int(input("Enter item"))
        Push(Stack,item)
    elif ch==2:
        item=Pop(Stack)
        if item=="Underflow":
            print("Underflow, Stack is empty")
        else:
            print("Popped item is",item)
    elif ch==3:
        item=Peek(Stack)
        if item=="Underflow":
            print("Underflow, Stack is empty")
        else:
            print("Topmost item is ",item)
    elif ch==4:
        Display(Stack)
    elif ch==5:
        break
    else:
        print("Invalid Choice")