Typing docs: increase prominence of warnings regarding @runtime_checkable
#127985
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JukkaL
reviewed
Dec 16, 2024
| @@ -2486,14 +2486,14 @@ types. | |||
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| .. warning:: | |||
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| Runtime-checkable protocols are known to be unsafe in several ways. | |||
| Runtime-checkable protocols are known to be unsound in several ways. | |||
| You should only use them for simple protocols, and even then only use | |||
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What about suggesting that they should only be used for method-only protocols? Or just for protocols with dunder methods -- since dunder methods typically have a well-understood signature, so the check is more likely to do the right thing at runtime?
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It isn't safe on even just dunder methods. An example of this is numpy arrays and __bool__, see other discussion about type checkers making unsafe assumptions related to this here
JelleZijlstra
approved these changes
Mar 3, 2025
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@AlexWaygood this has a conflict now, and some suggested wording changes. |
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We have some warnings in the docs for
typing.runtime_checkablealready, but:This PR makes the warnings more prominent and expands on the examples. It follows renewed discussion on how runtime-checkable protocols are fundamentally unsafe in many ways on the Discourse thread https://discuss.python.org/t/pep-767-annotating-read-only-attributes/73408
📚 Documentation preview 📚: https://cpython-previews--127985.org.readthedocs.build/