code: def nodes_iter(self, t=None, data=False):
          
          if t is not None:
              return iter([n for n in self.degree(t=t).values() if n > 0])
          return iter(self._node)
docs: Return an iterator over the nodes with respect to a given temporal snapshot.
  
          Parameters
          ----------
          t : snapshot id (default=None).
              If None the iterator returns all the nodes of the flattened graph.
          data : boolean, optional (default=False)
                 If False the iterator returns nodes.  If True
                 return a two-tuple of node and node data dictionary
  
          Returns
          -------
          niter : iterator
              An iterator over nodes.  If data=True the iterator gives
              two-tuples containing (node, node data, dictionary)
  
          Examples
          --------
          >>> G = dn.DynGraph()   # or DiGraph, MultiGraph, MultiDiGraph, etc
          >>> G.add_path([0,1,2], 0)
  
          >>> [n for n, d in G.nodes_iter(t=0)]
          [0, 1, 2]