Django Query __isnull=True or = None

They are equal:

>>> str(Person.objects.filter(age__isnull=True).query) == str(Person.objects.filter(age=None).query)
True
>>> print(Person.objects.filter(age=None).query)
SELECT "person_person"."id", "person_person"."name", "person_person"."yes", "person_person"."age" FROM "person_person" WHERE "person_person"."age" IS NULL
>>> print(Person.objects.filter(age__isnull=True).query)
SELECT "person_person"."id", "person_person"."name", "person_person"."yes", "person_person"."age" FROM "person_person" WHERE "person_person"."age" IS NULL

Exclusion: the Postgres JSON field (see the answer of @cameron-lee)

It depends on the type of field. As mentioned in other answers, they are usually equivalent but in general, this isn't guaranteed.

For example, the Postgres JSON field uses =None to specify that the json has the value null while __isnull=True means there is no json:

https://docs.djangoproject.com/en/3.0/ref/contrib/postgres/fields/#jsonfield