id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
28492	Allow defining expressions' default output_field as a class attribute rather than in __init__()	Mads Jensen	nobody	"There are a few expression-classes that override `__init__` just to set `output_field`, 

{{{
class Extent3D(GeoAggregate):

def __init__(self, expression, **extra):
    super().__init__(expression, output_field=ExtentField(), **extra)
}}}

From this comment https://github.com/django/django/pull/7611/files#r131567089 `runtests.py` needs to be adjusted, so it's possible to use a class-variable for the output field instead.
"	Cleanup/optimization	closed	Database layer (models, ORM)	dev	Normal	fixed		Simon Charette	Accepted	1	0	0	1	0	0