Simple Calculator Program in Python

```
Calculator Program

def add(x, y):
   return x + y

def subtract(x, y):
   return x - y

def multiply(x, y):
   return x * y

def divide(x, y):
   if y == 0:
      return "Error! Division by zero is not allowed."
   else:
      return x / y

print("Simple Calculator")
print("1. Addition")
print("2. Subtraction")
print("3. Multiplication")
print("4. Division")

while True:
   choice = input("Enter your choice (1/2/3/4): ")

   if choice in ('1', '2', '3', '4'):
      num1 = float(input("Enter first number: "))
      num2 = float(input("Enter second number: "))

      if choice == '1':
         print(num1, "+", num2, "=", add(num1, num2))

      elif choice == '2':
         print(num1, "-", num2, "=", subtract(num1, num2))

      elif choice == '3':
         print(num1, "*", num2, "=", multiply(num1, num2))

      elif choice == '4':
         print(num1, "/", num2, "=", divide(num1, num2))
      
      next_calculation = input("Do you want to do another calculation? (yes/no): ")
      if next_calculation.lower() != 'yes':
         break
   else:
      print("Invalid Input")
```