docs: def nx_gen_edge_attrs(G, key, edges=None, default=util_const.NoParam,
                        on_missing='error', on_keyerr='default'):
      """
      Improved generator version of nx.get_edge_attributes
  
      Args:
          on_missing (str): Strategy for handling nodes missing from G.
              Can be {'error', 'default', 'filter'}.  defaults to 'error'.
              is on_missing is not error, then we allow any edge even if the
              endpoints are not in the graph.
          on_keyerr (str): Strategy for handling keys missing from node dicts.
              Can be {'error', 'default', 'filter'}.  defaults to 'default'
              if default is specified, otherwise defaults to 'error'.
  
      Example:
          >>> # ENABLE_DOCTEST
          >>> from utool.util_graph import *  # NOQA
          >>> import utool as ut
          >>> G = nx.Graph([(1, 2), (2, 3), (3, 4)])
          >>> nx.set_edge_attributes(G, name='part', values={(1, 2): 'bar', (2, 3): 'baz'})
          >>> edges = [(1, 2), (2, 3), (3, 4), (4, 5)]
          >>> func = ut.partial(ut.nx_gen_edge_attrs, G, 'part', default=None)
          >>> #
          >>> assert len(list(func(on_missing='error', on_keyerr='default'))) == 3
          >>> assert len(list(func(on_missing='error', on_keyerr='filter'))) == 2
          >>> ut.assert_raises(KeyError, list, func(on_missing='error', on_keyerr='error'))
          >>> #
          >>> assert len(list(func(edges, on_missing='filter', on_keyerr='default'))) == 3
          >>> assert len(list(func(edges, on_missing='filter', on_keyerr='filter'))) == 2
          >>> ut.assert_raises(KeyError, list, func(edges, on_missing='filter', on_keyerr='error'))
          >>> #
          >>> assert len(list(func(edges, on_missing='default', on_keyerr='default'))) == 4
          >>> assert len(list(func(edges, on_missing='default', on_keyerr='filter'))) == 2
          >>> ut.assert_raises(KeyError, list, func(edges, on_missing='default', on_keyerr='error'))
      """
      if on_missing is None:
          on_missing = 'error'
      if default is util_const.NoParam and on_keyerr == 'default':
          on_keyerr = 'error'
  
      if edges is None:
          if G.is_multigraph():
              raise NotImplementedError('')
              # uvk_iter = G.edges(keys=True)
          else:
              edges = G.edges()
      # Generate `edge_data` edges and data dictionary
      if on_missing == 'error':
          edge_data = (((u, v), G.adj[u][v]) for u, v in edges)
      elif on_missing == 'filter':
          edge_data = (((u, v), G.adj[u][v]) for u, v in edges if G.has_edge(u, v))
      elif on_missing == 'default':
          edge_data = (((u, v), G.adj[u][v])
                       if G.has_edge(u, v) else ((u, v), {})
                       for u, v in edges)
      else:
          raise KeyError('on_missing={}'.format(on_missing))
      # Get `edge_attrs` desired value out of dictionary
      if on_keyerr == 'error':
          edge_attrs = ((e, d[key]) for e, d in edge_data)
      elif on_keyerr == 'filter':
          edge_attrs = ((e, d[key]) for e, d in edge_data if key in d)
      elif on_keyerr == 'default':
          edge_attrs = ((e, d.get(key, default)) for e, d in edge_data)
      else:
          raise KeyError('on_keyerr={}'.format(on_keyerr))
      return edge_attrs