Analyse an character if it is type in to an entry Widget.

[Norbert Haefke Freudenberg de]

Hi, 

I have need an idea how to analyse an character when it is type in to entry.

Description:

In my application are only numbers allowed.
If you type a number you get the result on the fly (in an other Widget). ( I
use the "change" signal of the entry widget)

So if you type any character from the keyboard it appears in the entry.
(Actually I analyse the character in the entry after it is displayed.)
But I like to analyse which type the character is befor it is displayed. 

I like prevent that any other charakter is displayed (and prozessed) then a
number.
Is there any way to analyse the character befor he is passed to the entry
Widget?


Thanks 

Norbert