some python functions

functions.py

def calc_avg(items):
  if not items:
    return 0
  total = sum(items)
  return  float(total)/len(items)


def std_deviation(items):
  if not items: return 0
  mean = calc_avg(items)
  variance = calc_avg([(x - mean)*(x - mean) for x in items])
  return math.sqrt(variance)