[web2py] How to check the extension of file from the controller

[Sanjeet Kumar]

I have the upload field in table i want to check the file extension from 
the controller during the upload i am using :-

SQLFORM.factory(db.emp_detail)
if form.accepts(request.vars, session):
         img = form.vars.image
if file.extension == 'something':
         update query