input: Write a function to calculate the maximum, minimum, and average values from a given sequence of numbers.
  
  def calculate_metrics(list):
      maximum = max(list)
      minimum = min(list)
      n = len(list)
      total = 0
      for num in list:
          total += num
      average = total/n
      return maximum, minimum, average
  
  assert calculate_metrics([3, 4, 5, 6, 21, 8])==(21, 3, 8.166666666666666)
output: def calculate_metrics(list):
      maximum = max(list)
      minimum = min(list)
      n = len(list)
      total = 0
      for num in list:
          total += num
      average = total/n
      return maximum, minimum, average