set_edge_attributes#

set_edge_attributes(G, values, name=None)[source]#

Sets edge attributes from a given value or dictionary of values.

Warning

The call order of arguments values and name switched between v1.x & v2.x.

Parameters:
GNetworkX Graph
valuesscalar value, dict-like

What the edge attribute should be set to. If values is not a dictionary, then it is treated as a single attribute value that is then applied to every edge in G. This means that if you provide a mutable object, like a list, updates to that object will be reflected in the edge attribute for each edge. The attribute name will be name.

If values is a dict or a dict of dict, it should be keyed by edge tuple to either an attribute value or a dict of attribute key/value pairs used to update the edge’s attributes. For multigraphs, the edge tuples must be of the form (u, v, key), where u and v are nodes and key is the edge key. For non-multigraphs, the keys must be tuples of the form (u, v).

namestring (optional, default=None)

Name of the edge attribute to set if values is a scalar.

Examples

After computing some property of the edges of a graph, you may want to assign a edge attribute to store the value of that property for each edge:

>>> G = nx.path_graph(3)
>>> bb = nx.edge_betweenness_centrality(G, normalized=False)
>>> nx.set_edge_attributes(G, bb, "betweenness")
>>> G.edges[1, 2]["betweenness"]
2.0

If you provide a list as the second argument, updates to the list will be reflected in the edge attribute for each edge:

>>> labels = []
>>> nx.set_edge_attributes(G, labels, "labels")
>>> labels.append("foo")
>>> G.edges[0, 1]["labels"]
['foo']
>>> G.edges[1, 2]["labels"]
['foo']

If you provide a dictionary of dictionaries as the second argument, the entire dictionary will be used to update edge attributes:

>>> G = nx.path_graph(3)
>>> attrs = {(0, 1): {"attr1": 20, "attr2": "nothing"}, (1, 2): {"attr2": 3}}
>>> nx.set_edge_attributes(G, attrs)
>>> G[0][1]["attr1"]
20
>>> G[0][1]["attr2"]
'nothing'
>>> 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:

>>> G = nx.Graph([(0, 1)])
>>> nx.set_edge_attributes(G, {(1, 2): {"weight": 2.0}})
>>> (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}
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