class_docstr: Class for incrementally computing the variance of a series of numbers.
class_docstr_tok: ["Class","for","incrementally","computing","the","variance","of","a","series","of","numbers","."]
code: def true_value(self):
      if self.ex2.value is None or self.ex.value is None:
          return None
      return max(0, self.ex2.value - self.ex.value**2)
  
imports: from abc import abstractmethod
  from typing import List
  from math import sqrt
  import numpy
label_desc: Use image node_id 4 for calling the Variance obj's underlying member method code with example usage: obj.true_value() and returns: max, None