import math


def compute_avg_dev(values):
  """ Compute the arithmetic mean and standard deviation of a list of values.
  Args:
    values Iterable of values
  Returns:
    Arithmetic mean, standard deviation
  """
  avg = sum(values) / len(values)
  var = 0
  for value in values:
    var += (value - avg) ** 2
  var /= len(values) - 1
  return avg, math.sqrt(var)