Ended up being a little more involved than I expected.. __getitem__ is left relatively intact for both TinyGraph and EdgeProxy, but __setitem__ needed to be modified for better error-handling (e.g. missing edges, poorly formatted requests). There's a weird edge case if you pass the same edge multiple times, but in opposite directions:

g = tg.TinyGraph(2)
g[[0, 1, 1], [1, 0, 0]] = [1, 2, 3]
# conflict??

I resolved this by reordering the vertex indices so that the first sequence always has the lower index, and this becomes equivalent to:

g[[0, 0, 0], [1, 1, 1]] = [1, 2, 3]
assert g.adjacency[0, 1] == g.adjacency[1, 0]
assert g.adjacency[0, 1] == 1 # I believe numpy breaks ties with the first value passed

which might still be weird, but at least numpy handles it for us and we still have a symmetric adjacency matrix. An alternate solution would be to set the elements of the adjacency matrix elementwise, but that requires extra casework (sequence/list vs int).