Add ThinGraph example to Multi*Graph doc_strings (#6160)

2 files changed, 42 insertions, 0 deletions

diff --git a/networkx/classes/multidigraph.py b/networkx/classes/multidigraph.py
index 31c33f67..81d2942f 100644
--- a/networkx/classes/multidigraph.py
+++ b/networkx/classes/multidigraph.py
@@ -269,6 +269,27 @@ class MultiDiGraph(MultiGraph, DiGraph):
     to_undirected_class : callable, (default: Graph or MultiGraph)
         Class to create a new graph structure in the `to_undirected` method.
         If `None`, a NetworkX class (Graph or MultiGraph) is used.
+
+    **Subclassing Example**
+
+    Create a low memory graph class that effectively disallows edge
+    attributes by using a single attribute dict for all edges.
+    This reduces the memory used, but you lose edge attributes.
+
+    >>> class ThinGraph(nx.Graph):
+    ...     all_edge_dict = {"weight": 1}
+    ...
+    ...     def single_edge_dict(self):
+    ...         return self.all_edge_dict
+    ...
+    ...     edge_attr_dict_factory = single_edge_dict
+    >>> G = ThinGraph()
+    >>> G.add_edge(2, 1)
+    >>> G[2][1]
+    {'weight': 1}
+    >>> G.add_edge(2, 2)
+    >>> G[2][1] is G[2][2]
+    True
     """
 
     # node_dict_factory = dict    # already assigned in Graph
diff --git a/networkx/classes/multigraph.py b/networkx/classes/multigraph.py
index 308c20cc..3d9e69b3 100644
--- a/networkx/classes/multigraph.py
+++ b/networkx/classes/multigraph.py
@@ -262,6 +262,27 @@ class MultiGraph(Graph):
     to_undirected_class : callable, (default: Graph or MultiGraph)
         Class to create a new graph structure in the `to_undirected` method.
         If `None`, a NetworkX class (Graph or MultiGraph) is used.
+
+    **Subclassing Example**
+
+    Create a low memory graph class that effectively disallows edge
+    attributes by using a single attribute dict for all edges.
+    This reduces the memory used, but you lose edge attributes.
+
+    >>> class ThinGraph(nx.Graph):
+    ...     all_edge_dict = {"weight": 1}
+    ...
+    ...     def single_edge_dict(self):
+    ...         return self.all_edge_dict
+    ...
+    ...     edge_attr_dict_factory = single_edge_dict
+    >>> G = ThinGraph()
+    >>> G.add_edge(2, 1)
+    >>> G[2][1]
+    {'weight': 1}
+    >>> G.add_edge(2, 2)
+    >>> G[2][1] is G[2][2]
+    True
     """
 
     # node_dict_factory = dict    # already assigned in Graph