issubclass() accept types (extension types and new-style classes), classic classes and arbitrary objects with the __bases__ attribute as its arguments. The latter was added in issue464992 [1] to support the Zope extension ExtensionClass.
I tested the current code of ExtensionClass [2], and seems it does not need that special support. Tests are passed on modified master which uses tp_bases instead of dynamical look up of __bases__, ExtensionClass.ExtensionClass is a subclass of type and ExtensionClass.Base is an instance of type, the code does not have the __bases__ property and does not set the __bases__ attribute explicitly. On other hand, the code in the Python core has a non-zero maintenance cost. It was rewritten several times for 19 years, there is a gigantic comment larger that the current code explaining it (and it is slightly outdated), and there was several bugs related to it [3] [4]. Should we continue to support non-type objects with __bases__ in issubclass()? If no, can we remove their support in 3.10 (it would fix a crash in issue41909) or after passing a deprecation period? [1] https://bugs.python.org/issue464992 [2] https://github.com/zopefoundation/ExtensionClass [3] https://bugs.python.org/issue39382 [4] https://bugs.python.org/issue41909 _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/2S2FM2J44H2FQTZZOC7MINFVMZMQKCOP/ Code of Conduct: http://python.org/psf/codeofconduct/
