pySilver

Interesting enough typical `replace` action does not have such side effects.

@jjconti so simply: ``` python def validate(self, attrs): subtype = attrs.get('subtype') promo_code = attrs.get('promo_code') date_start = attrs.get('date_start') date_end = attrs.get('date_end') if self.partial and self.instance: subtype = attrs.get('subtype', self.instance.subtype) promo_code =...

having callable parameter would be really nice addition. @Mathieson what approach you are using?