filters.py 文件源码

def choices(self):
        yield {
            'selected': self.lookup_exact_val == '' and not self.lookup_isnull_val,
            'query_string': self.query_string({},
                                              [self.lookup_exact_name, self.lookup_isnull_name]),
            'display': _('All'),
        }
        for pk_val, val in self.lookup_choices:
            yield {
                'selected': self.lookup_exact_val == smart_unicode(pk_val),
                'query_string': self.query_string({
                    self.lookup_exact_name: pk_val,
                }, [self.lookup_isnull_name]),
                'display': val,
            }
        if (is_related_field(self.field)
                and self.field.field.null or hasattr(self.field, 'rel')
                and self.field.null):
            yield {
                'selected': bool(self.lookup_isnull_val),
                'query_string': self.query_string({
                    self.lookup_isnull_name: 'True',
                }, [self.lookup_exact_name]),
                'display': EMPTY_CHANGELIST_VALUE,
            }