code: def stddev(self):
      
      if len(self) < 2:
        return float('NaN')
      # The stupidest algorithm, but it works fine.
      try:
        arr = self.samples()
        mean = sum(arr) / len(arr)
        bigsum = 0.0
        for x in arr:
          bigsum += (x - mean)**2
        return sqrt(bigsum / (len(arr) - 1))
      except ZeroDivisionError:
        return float('NaN')
docs: Return the sample standard deviation.