input: def understand_recursion():
      """This program is to understand recursion in Python.
      Define a recursive function to calculate the factorial of a number
      >>> factorial(5)
      120
      """
      def factorial(n):
          if n == 1:
              return 1
          else:
              return n * factorial(n - 1)
  
      result = factorial(5)
      print("Factorial of 5 is ", result)
  
      # Output: Factorial of 5 is 120
output:     understand_recursion()