I'm not entirely sure why the tests are failing

>>>classB:...     y=0...__slots__= ('z','foo')... >>> B().fod=1Traceback (most recent call last):  File "<stdin>", line 1, in <module>AttributeError: 'B' object has no attribute 'fod' and no __dict__ for setting new attributes. Did you mean: 'foo'?

AFAICT this should be the error that you get? Unless it's failing due to not being printed.

I'm not entirely sure why the tests are failing

>>>classB:...     y=0...__slots__= ('z','foo')... >>> B().fod=1Traceback (most recent call last):  File "<stdin>", line 1, in <module>AttributeError: 'B' object has no attribute 'fod' and no __dict__ for setting new attributes. Did you mean: 'foo'?

AFAICT this should be the error that you get? Unless it's failing due to not being printed.

@Gobot1234 The suggestion (Did you mean: 'foo'?) does not seem to be part of the error.

Should this perhaps check for__setattr__ overrides? There can be cases where the class has no__dict__ but some non slot attribute setting can still happen. In such a case this error might be misleading.

classFoo:__slots__= ("x","y")def__setattr__(self,name,val):ifname=="all":self.x=valself.y=valelse:super().__setattr__(name,val)f=Foo()f.all=5

@pablogsal since this is an error message change would you be willing to review?