"Don’t use len() on QuerySets" is too strong.

[Collin Anderson]

I've seen people write code like:

qs = Model.objects.filter(a=b)
if qs.count() >= 1:
    for q in qs:
        # do something with q

They think the that ".count()" call is more efficient, but it actually makes it slower. I asked the person about it they said: "the docs say don't use len() on querysets".

[Collin Anderson]

​https://github.com/django/django/pull/3961

[Tim Graham <timograham@…>]

In ee23e03637aa8b82311f93b0a660574a0512891a:

Fixed #24190 -- Clarified len(queryset)

[Tim Graham <timograham@…>]

In 09e8985f25ddd901a3678d4b34878d6c631b0cea:

[1.8.x] Fixed #24190 -- Clarified len(queryset)

Backport of ee23e03637aa8b82311f93b0a660574a0512891a from master

[Tim Graham <timograham@…>]

In 6dc6ec218860e4d4c5c1833c9b8607c4014c85d7:

[1.7.x] Fixed #24190 -- Clarified len(queryset)

Backport of ee23e03637aa8b82311f93b0a660574a0512891a from master