code: def std_dev(xs):
      
      m = mean(xs)  # this checks our pre-conditions, too
      return sqrt(sum((x - m) ** 2 for x in xs) / float(len(xs)))
docs: Returns the standard deviation of the given iterable of numbers.
  
      From http://rosettacode.org/wiki/Standard_deviation#Python
  
      An empty list, or a list with non-numeric elements will raise a TypeError.
  
      >>> std_dev([2,4,4,4,5,5,7,9])
      2.0
  
      >>> std_dev([9,10,11,7,13])
      2.0
  
      >>> std_dev([1,1,10,19,19])
      8.049844718999243
  
      >>> std_dev({1,1,10,19,19}) == std_dev({19,10,1})
      True
  
      >>> std_dev([10,10,10,10,10])
      0.0
  
      >>> std_dev([1,"b"])
      Traceback (most recent call last):
      ...
      ValueError: Input can't have non-numeric elements
  
      >>> std_dev([])
      Traceback (most recent call last):
      ...
      ValueError: Input can't be empty