Select network nodes with a given attribute value

Question

I'd like to select and perform operations on nodes within a graph with particular attributes. How would you select nodes with a given attribute value? For example:

P=nx.Graph()
P.add_node('node1',at=5)
P.add_node('node2',at=5)
P.add_node('node3',at=6)

Is there a way to select only the nodes with at == 5?.

I'm imagining something like (this doesn't work):

for p in P.nodes():
    P.node[p]['at'==5]

Answer 1

Python <= 2.7:

According to the documentation try:

nodesAt5 = filter(lambda (n, d): d['at'] == 5, P.nodes(data=True))

or like your approach

nodesAt5 = []
for (p, d) in P.nodes(data=True):
    if d['at'] == 5:
        nodesAt5.append(p)

Python 2.7 and 3:

nodesAt5 = [x for x,y in P.nodes(data=True) if y['at']==5]