How to get the point in time of (last) vertical retrace under Python?

I am using Pyga开发者_StackOverflow社区me to pageflip different stimuli on the screen. The problem is that pygame's flip function, although syncing the flip to the vertical retrace, does not tell me when the retrace was. Does anyone know of a way to get this information (preferably platform independent) in Python?

Regards, fladd

Just poll for the time immediately after the flip call, if that one syncs to the vertical retrace.