filters.py 文件源码

def choices(self):
        yield {
            'selected': (self.lookup_exact_val is '' and self.lookup_isnull_val is ''),
            'query_string': self.query_string({}, [self.lookup_exact_name, self.lookup_isnull_name]),
            'display': _('All'),
        }
        include_none = False
        for val in self.lookup_choices:
            if val is None:
                include_none = True
                continue
            val = smart_unicode(val)
            yield {
                'selected': self.lookup_exact_val == val,
                'query_string': self.query_string({self.lookup_exact_name: val},
                                                  [self.lookup_isnull_name]),
                'display': val,
            }
        if include_none:
            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,
            }