code: def append(self, value):
          
          self.count += 1
  
          if self.count == 1:
              self.old_m = self.new_m = value
              self.old_s = 0
          else:
              self.new_m = self.old_m + (value - self.old_m) / self.count
              self.new_s = self.old_s + (value - self.old_m) * (value - self.new_m)
  
              self.old_m = self.new_m
              self.old_s = self.new_s
docs: Append a value to the stats list
  
          Parameters
          ----------
          value : float
              The value to add