Import error: No module named zigbee

Hi,
Im trying to do a node discovery using this documentation: http://cms.digi.com/resources/documentation/digidocs/90001537/#references/r_ex_zb_discovery.htm%3FTocPath%3DModule%253A%2520xbee|_____9

The problem is that python doesnt recognise the module named zigbee. I suppose that i have to install some kind of library but I dont know which and how.

Thank you

What are you running this Python file on? It is meant to be running on a Digi X4 or X2 Gateway which has the default python.zip files on it.