docs: def _get_evidence(self, evidence_dict, time_slice, shift):
          """
          Getting the evidence belonging to a particular timeslice.
  
          Parameters:
          ----------
          evidence: dict
              a dict key, value pair as {var: state_of_var_observed}
              None if no evidence
  
          time: int
              the evidence corresponding to the time slice
  
          shift: int
              shifting the evidence corresponding to the given time slice.
          """
          if evidence_dict:
              return {(node[0], shift): evidence_dict[node] for node in evidence_dict if node[1] == time_slice}