Blender Exporter Query For Material Nodes

Hi all
Currently I , am writing a blender exporter for a third party software.
The problem is I, am not able to get the material node data applied on an object i.e. the material nodes created through the Node Editor.
I went through a lot of googling and the blender python API Docs but could not find a way to get material node data through python for Objects in the scene.
So, my conclusion is I, think the node related functions are unavailable in the Python API for Objects.
And if it thats not true then please help me out on this issue.

Thnx and Regards in Advance