Hi,
Given a `graph_tool.Edge` instance, is it possible to directly access the integer value (or its index value) of the source vertex and target vertex?
My current solution is
```
s = int(e.source())
t = int(e.target())
```
I have some function that calls the above routine many times and it is not fast enough. I am wondering if I can do it faster.
Similarly, can I access the index/integer value of a Vertex object directly?