Check if two vertices are connected in iGraph

For the record: are_connected (and also is_mutual and is_multiple that the poster has mentioned) are methods of the graph itself and not functions on their own, so the correct way to use them is as follows:

>>> g = Graph.GRG(100, 0.2)
>>> g.are_connected(0, 2)
False

GraphBase class has function get_eid(v1, v2, directed=True, error=True) that returns arbitrary edge between vertices specified by their indices. In you call it like this:

g.get_eid(v1, v2, directed=False, error=False)

it will return -1 if the vertices are disconnected, and some edge otherwise.