Re: [igraph] how to iterate a vertex seq to find neighbors

[Tamas Nepusz]

> btw, I see that get_eid(v1, v2) interprets v1 as the target node and
> v2 as the source node in a directed graph... is it intentional?
well, in fact, get_eid(v1, v2) interprets v1 as the source and v2 as  
the target. however, if the graph is directed and there is no v1 -->  
v2 edge, igraph also tries v2 --> v1 UNLESS you add "directed=True":

In [7]: g=Graph([(0,1),(1,2),(2,1)], directed=True)
In [8]: g.get_eid(0,1)
Out[8]: 0
In [9]: g.get_eid(1,0)
Out[9]: 0
In [10]: g.get_eid(1,2)
Out[10]: 1
In [11]: g.get_eid(2,1)
Out[11]: 2
In [12]: g.get_eid(1,0,directed=True)
InternalError: Error at ../../src/type_indexededgelist.c:1055: Cannot  
get edge id, no such edge, Invalid value

As you can see, g.get_eid(1,0) returns zero since there is no 1 --> 0  
edge but there is a 0 --> 1 edge whose index is zero, but  
g.get_eid(1,0,directed=True) throws an exception. This behaviour will  
change in 0.6, however, and the default value for directed= will be  
True as this is more logical.

--
Tamas