[Python-Dev] python and super (original) (raw)

Steven D'Aprano steve at pearwood.info
Fri Apr 15 03:23:52 CEST 2011

Ricardo Kirkner wrote:

I have a TestCase class, which inherits from both Django's TestCase and from some custom TestCases that act as mixin classes. So I have something like

class MyTestCase(TestCase, Mixin1, Mixin2): ... now django's TestCase class inherits from unittest2.TestCase, which we found was not calling super. Even if this is a bug and should be fixed in unittest2, this is an example where I, as a consumer of django, shouldn't have to be worried about how django's TestCase class is implemented. Since I explicitely base off 3 classes, I expected all 3 classes to be initialized, and I expect the setUp method to be called on all of them. If I'm assuming/expecting unreasonable things, please enlighten me.

If we treat django's failure to use super as a bug, you want the Python language to work-around that bug so that:

"I, as a consumer of django, shouldn't have to be worried about bugs in django". (For at least one class of bug.)

If we don't treat django's failure to use super as a bug, but as a deliberate design choice, then you are trying to do something which django doesn't support. Possibly deliberately doesn't support. You want the Python language to add that support so that:

"I, as a consumer of django, shouldn't have to be worried about whether django supports what I want to do or not".

Either way you look at it, I think it's extremely unreasonable to expect the language to work-around bugs in third-party applications, or to add features to them that the third-party developers either didn't consider or don't want.

Multiple inheritance is tricky enough to get right without adding "Do What I Mean" black magic to it. I'd rather work around bugs in third-party classes than try to deal with Python actively subverting the code I read and write by mysteriously calling superclass methods where there is no call to a superclass method.

-- Steven

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