<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def stddev(self):
 """Return the sample standard deviation."""

    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')