[docs] [issue37934] Docs: Clarify NotImplemented use cases
Vedran Čačić
report at bugs.python.org
Mon Sep 2 10:24:34 EDT 2019
Vedran Čačić <vedgar at gmail.com> added the comment:
Sorry, I think you still don't understand.
The emulation of double dispatch by single dispatch, with all complications it brings, is the only reason NotImplemented exists. If Python didn't have binary operators (or inheritance), I'm quite sure it wouldn't have NotImplemented. The idea was never "oh, this method isn't supported", but much more precise "this half of protocol, with given ordering of operands according to a class hierarchy, isn't implemented - try the other half".
Of course, you might argue that _once Python has NotImplemented_, it can be used elsewhere - but as I said, I don't think it should be encouraged.
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