[wxPython] intercept tab key in wxGrid

I need to intercept a "tab" key event in a wxGrid. The documentation omits
event handling for wxGrid. I tried EVT_CHAR, which seems to be ignored.

How do I do it?

I also would like to be able to use the grid cursor with the cursor keys -
however, at least with wxPython 2.3.2.1 on Linux this does not seem to
work by default. Why?

Thanks,
Horst