Hi all, In the `operator` module, both `operator.concat` and `operator.add` are described as performing `a + b`. When defining a type in pure python, it is not possible to give these different meanings. However, when defining a C extension type, it is possible to fill both `tp_as_number->nb_add` and `tp_as_sequence->sq_concat` with different implementations to obtain different behaviors.
Is the fact that `operator.concat` (`PySequence_Concat`) and `operator.add` (`PyNumber_Add`) can have different behaviors an implementation detail of CPython, or is it intended behavior in the language itself? I ask because [a recent PR for numpy][1] proposes implementing both of these slots, and discussion turned to whether it was intended to be possible to do this in the first place, and if so whether a patch will be needed to PyPy. It seems that there was at least some vague intent for this to be possible - In bpo-29139, Serhiy said > Third-party classes (maybe NumPy arrays, I don't know) can have different > implementations of `sq_concat` and `nb_add`. It seems to me there are at least three stances that could be taken here: * Specifying both is considered invalid: python should consider emitting a warning in `Type_READY` if both are filled. * Specifying both is considered an implementation detail specific to CPython: the [C API docs for the type slots][2] should indicate this * Specifying both is explicitly allowed and considered a language feature. `__concat__` should be added as a slot_wrapper around `sq_concat` to allow the language feature to be accessed without writing C extensions. Eric Wieser Apologies if this is not the right list - this didn't feel right for python-ideas or bpo. I'm more than happy to repost this elsewhere if asked. [1]: https://github.com/numpy/numpy/issues/16489 [2]: https://docs.python.org/3/c-api/typeobj.html _______________________________________________ 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/HCXMI7LPWZEKKPRIJTVHN5ZRWIUXM5C3/ Code of Conduct: http://python.org/psf/codeofconduct/
