class_docstr: Running mean calculator.
  
  This class can be used to calculate the mean of elements from a
  list, tuple, iterable or any other data source. The mean is
  calculated on the fly without explicitly summing the values,
  so it can be used for data sets with arbitrary item count. Also
  capable of returning the standard deviation (also calculated on
  the fly)
code: def __len__(self):
      return int(self._nitems)
  
imports: import math
label_desc: Use image node_id 14 for calling the RunningMean obj's underlying member method code with example usage: obj.__len__() and returns: int