code: def _expectation(self, _ID=slice(None)):
      expectation = self._posterior(_ID)
      expectation /= self.posterior_sum.unsqueeze(1)
      return expectation
  
imports: import collections
  import functools
  import io
  import os
  import warnings
  import dgl
  import numpy
  import scipy
  import torch
label_desc: Use image node_id 8 for calling the _Dirichlet obj's underlying member method code with example usage: obj._expectation(_ID) and returns: expectation