this class is not key value coding-compliant for the key numbersInput

If you are getting this error after doing the PyObjC averager tutorial called Using PyObjC for Developing Cocoa Applications with Python , import your class in main.py.

After the line:
import PyAveragerAppDelegate

add:
import Averager

This should allow the numbersInput variable to be properly bound to Interface Builder.

I found the solution on macosxhints forum here.