using Tix.FileSelectBox in python

[devnew]

hi
i was using Tix.FileSelectBox to select imagefiles from a
directory..when i click on image and click my app's okbutton i can
get the selected image name by

self.selimgname=self.myfileselectbox.selection.cget("value")

after this if i just select a folder and not an image and click
ok then again the myfileselectbox.selection.cget("value") gives
the previously selected image name.

i would like to give an error msg asking the user if he doen't select
an image..how can i do this?

devnew