On Tue, Jul 5, 2016, at 11:50, Steven D'Aprano wrote: > If PyDict_SetItem expects an actual dict (accept no substitutes or > subclasses), why is there no error? I would have expected a segfault at > worst or at least an exception.
Subclasses are fine. Sort of. In general if you pass a *subclass* of [say] dict to a built-in method that is expecting a real dict, the effect is that the assignments will go straight through to the real dict, and never call any overridden method. I.e. it's as if you called dict.__setitem__(self, key, value). Something your own __setitem__ method may have done [directly or via super()] anyway... or may not have. So any special logic in your own __setitem__, which may have included e.g. copying it to an alternate place, changing the key or value, or simply refusing to add the item to the dictionary at all, will be ignored, and your object may end up in an inconsistent state. -- https://mail.python.org/mailman/listinfo/python-list
