code: def predecessors_iter(self, n, t=None):
          
          try:
              if t is None:
                  return iter(self._pred[n])
              else:
                  return iter([i for i in self._pred[n] if self.__presence_test(i, n, t)])
          except KeyError:
              raise nx.NetworkXError("The node %s is not in the graph." % (n,))
docs: Return an iterator over predecessors nodes of n at time t (optional).
  
          Parameters
          ----------
          n : node
              Nodes can be, for example, strings or numbers.
              Nodes must be hashable (and not None) Python objects.
          t : snapshot id (default=None)
              If None will be returned the presence of the interaction on the flattened graph.