Updated networkx/classes/function.py . Solves Issue #5463 (#5474)

* Updated networkx/classes/function.py

* Reformatted using black

* Update networkx/classes/function.py

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

* Update networkx/classes/function.py

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

* Update networkx/classes/function.py

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

* Applying style manually

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

* Apply style manually

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>

* Added example

* Updated

* Update case of multigraph and case of using G.edges to set H

* format doc_string example

Co-authored-by: Ross Barnowski <rossbar@berkeley.edu>
Co-authored-by: Dan Schult <dschult@colgate.edu>

1 files changed, 28 insertions, 0 deletions

diff --git a/networkx/classes/function.py b/networkx/classes/function.py
index 7707ec4c..fb24105f 100644
--- a/networkx/classes/function.py
+++ b/networkx/classes/function.py
@@ -786,6 +786,11 @@ def set_edge_attributes(G, values, name=None):
         >>> G[1][2]["attr2"]
         3
 
+    The attributes of one Graph can be used to set those of another.
+
+        >>> H = nx.path_graph(3)
+        >>> nx.set_edge_attributes(H, G.edges)
+
     Note that if the dict contains edges that are not in `G`, they are
     silently ignored::
 
@@ -794,6 +799,29 @@ def set_edge_attributes(G, values, name=None):
         >>> (1, 2) in G.edges()
         False
 
+    For multigraphs, the `values` dict is expected to be keyed by 3-tuples
+    including the edge key::
+
+        >>> MG = nx.MultiGraph()
+        >>> edges = [(0, 1), (0, 1)]
+        >>> MG.add_edges_from(edges)  # Returns list of edge keys
+        [0, 1]
+        >>> attributes = {(0, 1, 0): {"cost": 21}, (0, 1, 1): {"cost": 7}}
+        >>> nx.set_edge_attributes(MG, attributes)
+        >>> MG[0][1][0]["cost"]
+        21
+        >>> MG[0][1][1]["cost"]
+        7
+
+    If MultiGraph attributes are desired for a Graph, you must convert the 3-tuple
+    multiedge to a 2-tuple edge and the last multiedge's attribute value will
+    overwrite the previous values. Continuing from the previous case we get::
+
+        >>> H = nx.path_graph([0, 1, 2])
+        >>> nx.set_edge_attributes(H, {(u, v): ed for u, v, ed in MG.edges.data()})
+        >>> nx.get_edge_attributes(H, "cost")
+        {(0, 1): 7}
+
     """
     if name is not None:
         # `values` does not contain attribute names