Allow first argument to be passed as kwarg in dispatcher (#6471)

* tweak _dispatch to allow func(G=G) pattern in signature

Co-authored-by: Erik Welch <erik.n.welch@gmail.com>

2 files changed, 21 insertions, 1 deletions

diff --git a/networkx/classes/backends.py b/networkx/classes/backends.py
index 183db170..c96f4896 100644
--- a/networkx/classes/backends.py
+++ b/networkx/classes/backends.py
@@ -128,7 +128,13 @@ def _dispatch(func=None, *, name=None):
 
     @functools.wraps(func)
     def wrapper(*args, **kwds):
-        graph = args[0]
+        if args:
+            graph = args[0]
+        else:
+            try:
+                graph = kwds["G"]
+            except KeyError:
+                raise TypeError(f"{name}() missing positional argument: 'G'") from None
         if hasattr(graph, "__networkx_plugin__") and plugins:
             plugin_name = graph.__networkx_plugin__
             if plugin_name in plugins:
diff --git a/networkx/classes/tests/test_backends.py b/networkx/classes/tests/test_backends.py
new file mode 100644
index 00000000..8d0c86a4
--- /dev/null
+++ b/networkx/classes/tests/test_backends.py
@@ -0,0 +1,14 @@
+import pytest
+
+import networkx as nx
+
+pytest.importorskip("scipy")
+pytest.importorskip("numpy")
+
+
+def test_dispatch_kwds_vs_args():
+    G = nx.path_graph(4)
+    nx.pagerank(G)
+    nx.pagerank(G=G)
+    with pytest.raises(TypeError):
+        nx.pagerank()