code: def plot(self, ax=None):
      # validate keys are the same
      diff = dict()
  
      for key, value in self.counts[0].items():
          diff[key] = value - self.counts[1][key]
  
      if ax is None:
          _, ax = plt.subplots()
  
      ax.bar(
          list(range(len(diff))), list(diff.values()), color=self.color
      )
      ax.set_xticks(list(range(len(diff))), diff.keys())
  
      # remember to set these attributes
      self.ax_ = ax
      self.figure_ = ax.figure
  
      ax.set_ylabel("Count")
  
      # remember to return self
      return self
  
imports: from collections import Counter
  import numpy
  import matplotlib.pyplot
  from sklearn_evaluation import __version__
  from sklearn_evaluation.plot.plot import AbstractComposedPlot, AbstractPlot
label_desc: Use image node_id 2 for calling the MyBarSub obj's underlying member method code with example usage: obj.plot(ax) and returns: self