input: def understand_recursion():
      """Develop a Python program to clearly understand the concept of recursion.
      >>> def factorial(n):
      ...     if n == 1:
      ...         return 1
      ...     else:
      ...         return n * factorial(n - 1)
      >>> result = factorial(5)
      >>> print("Factorial of 5 is ", result)
      Factorial of 5 is 120
      """
output:     def factorial(n):
          if n == 1:
              return 1
          else:
              return n * factorial(n - 1)
      result = factorial(5)
      print("Factorial of 5 is ", result)