>From release 0.5, the C core of the igraph library is not included
in the Python distribution - you must compile and install the C core
separately. Windows installers already contain a compiled igraph DLL,
so they should work out of the box. Linux users should refer to the
igraph homepage for
compilation instructions (but check your distribution first, maybe
there are pre-compiled packages available). OS X users may
benefit from the disk images in the Python Package Index.
Unofficial installers for 64-bit Windows machines and/or different Python
versions can also be found here.
Many thanks to the maintainers of this page!