class_docstr: Statistic tracking the count, mean, and (diagonal) variance of a single
  :class:`torch.Tensor`.
code: def __init__(self):
      self.shape = None
      self.welford = WelfordCovariance(diagonal=True)
      super().__init__()
  
imports: import copy
  from abc import ABC, abstractmethod
  from collections import defaultdict
  from typing import Any, Callable, Dict, Hashable, Union
  import torch
  from pyro.ops.welford import WelfordCovariance
label_desc: Use image node_id 1 to create a new CountMeanVarianceStats object from inherited base classes: StreamingStats with example: obj = CountMeanVarianceStats()