i want to change field size attribute dynamically if user define 15 then digit limit should be 15 if user define 10 then field size should be 10 

any solution you suggest pls ..

what i'm doing 

```

@api.multi 

 @api.onchange('id_proof') 

 def _id_proof_onchange(self):

 return {'attrs': {'id_proof_no': [('size', '=', self.id_proof.digit_limit)]}}

```

no result