__contains__ on an incompletely evaluated QuerySet can incorrectly return False

[Kevin Michel]

The bug is in the function QuerySet.__contains__(self, val), which is executed when using the python operator in.

It can only happen if :

• val is in the QuerySet
• val is the last item of the QuerySet
• the QuerySet has not been completely evaluated

If all those conditions hold, then :

• val is not yet in self._result_cache
• self._iter is not None

This makes us jump to the while True loop, which runs correctly until we fetch the last item using self._fill_cache(num=1).

When fetching the last item, inside the self._fill_cache function, self._iter is set to None.

Just after fetching the last item, but before comparing its value against val, self.__contains__ checks the value of self._iter, which is None, and incorrectly return False.

The value of the last item should have been checked before checking the value of self._iter.

[Kevin Michel]

Actually, after trying to write a test for the bug, I think the bug does not really exist.

During the "self._fill_cache(num=1)", self._iter will be set to None only if no element has been added to the _result_cache, in which case there is no new element to compare against val.

Sorry for the false alarm.

[Aymeric Augustin]

As indicated by kmichel_wgs. Please re-open if you can provide a test case. Thanks!