Slicing an EmptyQuerySet gives a list, not another EmptyQuerySet

[Forest Bond]

This causes problems if you want to do, for example, qs[0:1].get(), which is, arguably, poor form. Still, I think this is a bug.

In [25]: type(models.TestRun.objects.none()[0:10])
Out[25]: <type 'list'>

In [26]: type(models.TestRun.objects.all()[0:10])
Out[26]: <class 'django.db.models.query.QuerySet'>

[Malcolm Tredinnick]

This isn't quite as clear as it looks. Slicing a normal QuerySet will sometimes return a list as well; it depends upon whether the results have already been retrieved from the database or not.

Probably the solution here is a documentation one, but it's worth thinking about what else might be possible. Always returning a QuerySet, though, is, from memory, a little fiddly to organise efficiently and always correctly.

[Ori Livneh]

document which type will be returned when slicing a QuerySet

[Ori Livneh]

EmptyQuerySet is a red herring -- the list is being returned by __getitem__ on the superclass, which is QuerySet. The real problem is that the documentation for QuerySet doesn't currently do a good job explaining what type object slicing a QuerySet returns. I've added a patch to improve the documentation on this topic.

[Claude Paroz]

Don't forget to fix the double 'a' before the commit (Slicing a a QuerySet).

[Aymeric Augustin]

In fact there's no such thing as an unevaluated EmptyQuerySet: __init__ sets self._result_cache = [].

[Aymeric Augustin]

In [17383]:

Fixed #10139 -- Clarified that slicing an evaluated QuerySet returns a list, not a QuerySet. Thanks ori for the patch.