admin.SimpleListFilter should fill used_parameters before doing lookups

[ronnie@…]

I had a case where i needed the self.value() in the lookup function. But the value is empty because the init function first does the lookup and then fills the used_parameters.

I have overwritten the init function in my superclass, but i think they could be switched safely

[chrismedrela]

@Ronnie, thank you for your input. Could you create a pull request? BTW What is your case that you need self.value() in the lookup function?

[Vajrasky Kok]

Let's use the example from Django documentation (​https://docs.djangoproject.com/en/dev/ref/contrib/admin/). We have two filters (80's and 90's). I imagine Ronnie had this scenario:

When you click 80's, the filter would be transformed to:
80-85
86-89
90's

When you click 90's, the filter would be transformed to:
80's
90-95
96-99

The default filters are of course:
80's
90's

[Vajrasky Kok]

Here is the PR: ​https://github.com/django/django/pull/1896

This feature is not convincing. But the change is trivial. So I leave to core developers whether they want to incorporate this feature or not.

[chrismedrela]

In my opinion the patch looks really good. There are only minor issues like PEP8 -- see my comments on the PR.

[Vajrasky Kok]

Updated PR based on Chris Medrela's review.

[Anssi Kääriäinen]

It seems like the change is safe to do. While I don't see huge need for this change, this change is useful to at least the ticket's reporter & reviewer.

I'll do final polish & commit.

[Anssi Kääriäinen <akaariai@…>]

In 68b540c97751f052a7622a7ab80a32a7d89d2aa2:

Fixed #21361 -- allowed access self.value() from SimpleListFilter lookup

Reviewed by Chris Medrela.