Copying widget image to pixmap

[Jay Bloodworth <jay dokodiner com>]

Can anyone give me some pointers on an appropriate idiom for making a
widget display a representation of itself to an offscreen drawable such
as a pixmap?  I would think this is not an unheard of operation, yet I
can't find any publically available interfaces to do it.  For bonus
points, I actually need the resulting image in the form of a pixmap /
transparency bitmap pair.  For double bonus points, I'm working  in
pygtk, though I can translate a C-based answer prettily easily.

Thanks in advance,
Jay