input: Write a function to calculate the maximum, minimum, and average values from a given sequence of numbers. The function should return the maximum, minimum, and average values as a tuple.
  def calculate_metrics(list):
      maximum = max(list)
      minimum = min(list)
      n = len(list)
      total = sum(list)
      average = total/n
      return maximum, minimum, average
  
  assert calculate_metrics([3, 4, 5, 6, 21, 8])==(21, 3, 8.166666666666666)
  assert calculate_metrics([1, 2, 3, 4, 5])==(5, 1, 3.0)
  assert calculate_metrics([10, 20, 30, 40, 50])==(50, 10, 30.0)
  assert calculate_metrics([99, 1, 5, 77, 88])==(99, 1, 54.0)
  assert calculate_metrics([])==(None, None, None)
output: def calculate_metrics(list):
      if not list:
          return None, None, None
      maximum = max(list)
      minimum = min(list)
      n = len(list)
      total = sum(list)
      average = total/n
      return maximum, minimum, average