input: 
  def calculate_mean(numbers):
      """
      Calculate the average of numbers stored in an array.
      >>> calculate_mean([10, 20, 30])
      20.0
      """
      total_sum = 0
      for num in numbers:
          total_sum += num
      mean = total_sum / len(numbers)
      return mean
  
output:     total_sum = 0
      for num in numbers:
          total_sum += num
      mean = total_sum / len(numbers)
      return mean