Stack in Python

def push(STACK,item):
    STACK.append(item)

def is_empty(STACK):
    if len(STACK)==0:
        return True
    else:
        return False

def pop(STACK):
    if is_empty(STACK)==True:
        ret="STACK UNDERFLOW"
        print("STACK UNDERFLOW")
    else:
        ret=STACK.pop()
    return ret

def display(STACK):
    if is_empty(STACK)==True:
        print("STACK IS EMPTY")
    else:
        print("The elements of the stack are")
        for i in range(len(STACK)-1,-1,-1):
            print(STACK[i])

def peek(STACK):
    if is_empty(STACK)==True:
        ret="STACK UNDERFLOW"
    else:
        ret=STACK[len(STACK)-1]
    return ret

# Stack is initially empty
STACK = []

while True:
    print("\nStack Options")
    print("1. Push")
    print("2. Pop")
    print("3. Display Stack")
    print("4. Peek")
    print("5. Exit")
    choice = int(input("Enter your choice (1-5): "))
    if choice == 1:
        item = int(input("Enter the item: "))
        push(STACK, item)
    elif choice == 2:
        item = pop(STACK)
        if item != "STACK UNDERFLOW":
            print(item, "was deleted from the stack")
        else:
            print("STACK UNDERFLOW")
    elif choice == 3:
        display(STACK)
    elif choice == 4:
        item = peek(STACK)
        print(item, "is present at the top of the stack")
    elif choice == 5:
        break
    else:
        print("Invalid choice")