input:     def calculate_mean(numbers):
          """Calculates the average of numbers stored in an array.
  
          >>> calculate_mean([10, 20, 30])
          20
          """
          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