Implementation of Stack in Python List

#Function to check the stack is empty or not.

def isEmpty(stk):

    if stk==[]:

        return True

    else:

        return False

#Function to push the value in the stack.

def Push(stk,val):

    stk.append(val)

    top=len(stk)-1

#Function to remove the value from the top of the stack

def Pop(stk):

    if isEmpty(stk):

        return "Underflow"

    else:

        val=stk.pop()

        if len(stk)==0:

            top=None

        else:

            top=len(stk)-1

        return val

#Function to inspect the position of the top to insert value in stack

def Peek(stk):

    if isEmpty(stk):

        return "Underflow"

    else:

        top=len(stk)-1

        return stk[top]

#Function to display the stack values

def Display(stk):

    if isEmpty(stk):

        print("Stack is Empty, Nothing to display")

    else:

        top=len(stk)-1

        print(stk[top],"<-top")

        for i in range(top-1,-1,-1):

            print(stk[i])

#__main__

Stack=[]        #Initially stack is empty list

top=None

while True:

    print("STACK OPERATION MENU")

    print("1. Push")

    print("2. Pop")

    print("3. Peek")

    print("4. Display")

    print("5. Exit")

    ch=int(input("Enter your choice: "))

    if ch==1:

        n=int(input("Enter value: "))

        Push(Stack,n)

    elif ch==2:

        n=Pop(Stack)

        if n=="Underflow":

            print("Underflow!!! Stack is empty")

        else:

            print("Popped value is:",n)

    elif ch==3:

        n=Peek(Stack)

        if n=="Underflow":

            print("Underflow!!! Stack is empty")

        else:

            print("Topmost value is:",n)

    elif ch==4:

        Display(Stack)

    elif ch==5:

        break;

    else:

        print("Invalid choice")

Output:

STACK OPERATION MENU

1. Push

2. Pop

3. Peek

4. Display

5. Exit

Enter your choice: