DS STACK.py

S=[] #stack
top=None
def isEmpty(stk):
    "Returns if a stack is empty or not"

    # return stk==[]
    if stk==[]:
        return True
    else:
        return False


def push(stk,item):

    stk.append(item)
    top=len(stk)-1

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


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


def display(stk):
    if isEmpty(stk):
        print("Underflow")
    else:
        top=len(stk)-1
        print(stk[top],"<----TOP")
        for i in range(top-1,-1,-1):
            print(stk[i])


if __name__=="__main__":
    while True:
        print("STACK IMPLEMENTATION")
        print("1.PUSH")
        print("2.POP")
        print("3.DISPLAY")
        print("4.PEEK")
        print("5.EXIT")
        chs=[1,2,3,4,5]
        ch=int(input("Enter your choice(1-5):\n"))
        if ch in chs:
            if ch==1:
                i=int(input("Enter your number:\n"))
                push(S,i)
                print(f"succesfully pushed {i}")
                input("press any key to continue")

            elif ch==2:
                # i=int(input("Enter your number:\n"))/
                item=s_pop(S)
                if item=="Underflow":
                    print("Underflow ! cannot pop the stack")
                else:

                    print(f"succesfully popped {item}" )
                input("press any key to continue")
            elif ch==3:
                # i=int(input("Enter your number:\n"))
                display(S)
                input("press any key to continue")

            elif ch == 4:
                print(peek(S))
                input("press any key to continue")

            elif ch == 5:
                quit()