fix: model serializer instance should not be sequence

[JoshFerge]

fixes #718

[sobolevn]

I could not find any Sequence usages in https://github.com/encode/django-rest-framework/blob/master/rest_framework/serializers.py

Thanks!

[JoshFerge]

I could not find any Sequence usages in https://github.com/encode/django-rest-framework/blob/master/rest_framework/serializers.py

Thanks!

just fixed the type ignore error in ci

[intgr]

instance is a sequence when the serializer is initialized with many=True. Although it truly is annoying to deal with.

There was a plan to fix this with an overloaded Serializer __new__ method, but it requires changes to mypy:

• Honor return type of __new__ even if not a subclass python/mypy#15182

[JoshFerge]

got it. thanks for clarifying! will close.

[JoshFerge]

Re-opening, as I think that internally the type will never be a sequence, as the new function will return a ListSerializer if a sequence is passed in. I think this is correct.

As written, the serializer is impossible to write a subclass for. cc @intgr @sobolevn

[intgr]

Sorry for the lack of reply. It's a tricky decision between two bad options and I've been pondering this in the background. I'm rather inclined to merge this.