Get the user-specified Evidence codes. Return smaller set: include/exclude

def get_min_inc_exc(self, inc_set=None, exc_set=None):
        """Get the user-specified Evidence codes. Return smaller set: include/exclude"""
        if inc_set is None and exc_set is None:
            return {}
        inc = self.get_evcodes(inc_set, exc_set)
        exc = set(self.code2nt.keys()).difference(inc)
        return {'inc':inc} if len(inc) <= len(exc) else {'exc': exc}