> Python is very much a language about responsibility.  If Django is overriding `__getattribute__` then it is their responsibility to ensure that everything still works properly.

Perhaps I didn't stress observability enough. A tool like a tracer or a profiler, in the ideal world, is not supposed to perturb the tracee in any way. The current implementation of isinstance, when used by an observability tool, may cause side effects as well as overheads, so it is not safe to use in such tools. Working around it may solve the side-effects issue, but leaves the problem of overheads. Changing the way isinstance works internally might prove beneficial for such tools.

En passant,  I think it should be noted that the built-in "type" doesn't suffer from the same problem, i.e.

~~~
class Side(object):
    def __getattribute__(self, name):
        ValueError(name)


type(Side())
~~~

works as expected.