Allow classes to relabel nodes -- casting (#5903)

1 files changed, 6 insertions, 2 deletions

diff --git a/networkx/relabel.py b/networkx/relabel.py
index 35e71536..65297d57 100644
--- a/networkx/relabel.py
+++ b/networkx/relabel.py
@@ -114,9 +114,13 @@ def relabel_nodes(G, mapping, copy=True):
     --------
     convert_node_labels_to_integers
     """
-    # you can pass a function f(old_label)->new_label
+    # you can pass a function f(old_label) -> new_label
+    # or a class e.g. str(old_label) -> new_label
     # but we'll just make a dictionary here regardless
-    if not hasattr(mapping, "__getitem__"):
+    # To allow classes, we check if __getitem__ is a bound method using __self__
+    if not (
+        hasattr(mapping, "__getitem__") and hasattr(mapping.__getitem__, "__self__")
+    ):
         m = {n: mapping(n) for n in G}
     else:
         m = mapping