[PyQt] How to trigger refresh of background window

[Ian]

Hi all,

How can I cause a repaint event on a window that is not the current focus?

When I click on the window it comes to the front, repaints itself and 
shows the (changed) data correctly.

However in my use case, data shown in the background window, has been 
updated in another window, and I want to update the background window 
(without activating it or scribbling on the screen where I shouldn't).  
Is this possible?

I'm using PyQt on Windows 7.

Thanks

Ian