How to make a calculator using Python?

Code to make a calculator in Python is:

op = input("Enter a Operator you want to use"
            "+,-,*,/\n")
if op=='+':
    print("Enter 1st number")
    a1 = int(input())
    print("Enter 2st number")
    a2 = int(input())
    print(" Sum is ",int(a1) + int(a2))
elif op=='-':
    print("Enter 1st number")
    a1 = int(input())
    print("Enter 2st number")
    a2 = int(input())
    print(" Sum is ", int(a1) - int(a2))
elif op=='*':
    print("Enter 1st number")
    a1 = int(input())
    print("Enter 2st number")
    a2 = int(input())
    print(" Sum is ", int(a1) * int(a2))
elif op=='/':
    print("Enter 1st number")
    a1 = int(input())
    print("Enter 2st number")
    a2 = int(input())
    print(" Sum is ", int(a1) / int(a2))
else:
    print("Enter valid operator")

Output: