formEncode - complicate validate form

Hi all. I'm using formEncode to validate my forms, and I'm 
stopped
on how to do a complicated validation that depened on what forms
element was filled. I mean I want to validate file that is 
uploaded but only when the checkbox on the form is checked. How 
to do this?
In python code this looks like:

if form.radio is checked:
    #validate file form that i uploaded
    code...
else:
    #validate other forms fields
    if form.login != '' and form.password !='':
	code..
    else:
	code..

I write my own class to validate file but file is not always sent 
so it must be validate depend on other form's field are checked. 
Thanks for any help
Gregor
 

----------------------------------------------------
Jan Garbarek w Polsce 3-8 czerwca 2006 - Gdansk, Koszalin,
Poznan, Bydgoszcz, Szczecin, Wroclaw - więcej informacji: 
http://klik.wp.pl/?adr=www.JanGarbarek.pl&sid=757




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