code: def sd(xs):
      """Returns the standard deviation of an iterable.
  
      Example:
  
          >>> sd([1, 4, 7, 11])       #doctest:+ELLIPSIS
          4.2720...
  
      @param xs: an iterable yielding numbers.
      @return: the standard deviation of the numbers provided by the iterable.
  
      @see: RunningMean() if you also need the mean
      """
      return RunningMean(xs).sd
  
imports: import math
label_desc: Use image node_id 6 for calling a global function with example usage: sd(xs) and returns: RunningMean