code: def union_all(graphs, rename=()):
      """Returns the union of all graphs.
  
      The graphs must be disjoint, otherwise an exception is raised.
  
      Parameters
      ----------
      graphs : iterable
         Iterable of NetworkX graphs
  
      rename : iterable , optional
         Node names of graphs can be changed by specifying the tuple
         rename=('G-','H-') (for example).  Node "u" in G is then renamed
         "G-u" and "v" in H is renamed "H-v". Infinite generators (like itertools.count)
         are also supported.
  
      Returns
      -------
      U : a graph with the same type as the first graph in list
  
      Raises
      ------
      ValueError
         If `graphs` is an empty list.
  
      NetworkXError
          In case of mixed type graphs, like MultiGraph and Graph, or directed and undirected graphs.
  
      Notes
      -----
      For operating on mixed type graphs, they should be converted to the same type.
      >>> G = nx.Graph()
      >>> H = nx.DiGraph()
      >>> GH = union_all([nx.DiGraph(G), H])
  
      To force a disjoint union with node relabeling, use
      disjoint_union_all(G,H) or convert_node_labels_to integers().
  
      Graph, edge, and node attributes are propagated to the union graph.
      If a graph attribute is present in multiple graphs, then the value
      from the last graph in the list with that attribute is used.
  
      Examples
      --------
      >>> G1 = nx.Graph([(1, 2), (2, 3)])
      >>> G2 = nx.Graph([(4, 5), (5, 6)])
      >>> result_graph = nx.union_all([G1, G2])
      >>> result_graph.nodes()
      NodeView((1, 2, 3, 4, 5, 6))
      >>> result_graph.edges()
      EdgeView([(1, 2), (2, 3), (4, 5), (5, 6)])
  
      See Also
      --------
      union
      disjoint_union_all
      """
      R = None
      seen_nodes = set()
  
      # rename graph to obtain disjoint node labels
      def add_prefix(graph, prefix):
          if prefix is None:
              return graph
  
          def label(x):
              return f"{prefix}{x}"
  
          return nx.relabel_nodes(graph, label)
  
      rename = chain(rename, repeat(None))
      graphs = (add_prefix(G, name) for G, name in zip(graphs, rename))
  
      for i, G in enumerate(graphs):
          G_nodes_set = set(G.nodes)
          if i == 0:
              # Union is the same type as first graph
              R = G.__class__()
          elif G.is_directed() != R.is_directed():
              raise nx.NetworkXError(
                  "All graphs must be directed or undirected."
              )
          elif G.is_multigraph() != R.is_multigraph():
              raise nx.NetworkXError(
                  "All graphs must be graphs or multigraphs."
              )
          elif not seen_nodes.isdisjoint(G_nodes_set):
              raise nx.NetworkXError(
                  "The node sets of the graphs are not disjoint.\n"
                  "Use `rename` to specify prefixes for the graphs or use\n"
                  "disjoint_union(G1, G2, ..., GN)."
              )
  
          seen_nodes |= G_nodes_set
          R.graph.update(G.graph)
          R.add_nodes_from(G.nodes(data=True))
          R.add_edges_from(
              G.edges(keys=True, data=True)
              if G.is_multigraph()
              else G.edges(data=True)
          )
  
      if R is None:
          raise ValueError("cannot apply union_all to an empty list")
  
      return R
  
imports: from itertools import chain, repeat
  import networkx
label_desc: Use image node_id 1 for calling a global function with example usage: union_all(graphs, rename) and returns: R, nx, graph, prefix, x