[igraph] Union of two graphs keeping attributes

[Matteo Fortini]

Hi,
regarding a question which was asked before in this ML by Gábor Tóth,
you can find my solution here, which works, but is still too slow for
me:

http://stackoverflow.com/questions/16928593/igraph-python-union-preserving-attributes

Hope someone can find a way to speed it up.

Thanks,
Matteo