Yeah, I have to agree with Neil. I had exactly this issue a couple years ago, and it took me an hour or two to figure out that it was a property/descriptor-protocol causing the issue, at which point the fix became trivial. Just knowing to think "it's a property, stupid!" was the hard part and just stating that in the error message would have saved me the frustration.
On Fri, Feb 11, 2022 at 2:46 AM Neil Girdhar <mistersh...@gmail.com> wrote: > I humbly disagree that any of what you wrote is "obvious". > > On Fri, Feb 11, 2022 at 4:41 AM Steven D'Aprano <st...@pearwood.info> > wrote: > >> On Thu, Feb 10, 2022 at 02:27:42PM -0800, Neil Girdhar wrote: >> >> > AttributeError: can't set attribute 'f' >> > >> > This can be a pain to debug when the property is buried in a base class. >> >> > Would it make sense to mention the reason why the attribute can't be >> set, >> > namely that it's on a property without a setter? >> >> I have no objection to changing the error message, I'm sure it's a small >> enough change that you should just open a ticket on b.p.o. for it. But I >> don't expect that it will be particularly useful either. >> >> If you can't set an attribute on an object, aren't there three obvious >> causes to check? >> >> - the object has no __dict__, and so has no attributes at all; >> e.g. trying to set an attribute on a float; >> >> - the object has slots, but 'f' is not one of them; >> >> - or 'f' is a property with no setter (or a setter that raises >> AttributeError). >> >> Have I missed any common cases? >> >> The error messages are different in each case, but even if they were the >> same, there are three obvious causes to check, and property is one of >> them. >> >> I suppose that there are exotic failures that could happen in >> __getattribute__ or weird descriptors, or metaclass magic, etc, and >> *those* might be hard to debug, but it doesn't seem likely to me that a >> read-only property will be mysterious. >> >> Especially if you have the object available in the interactive >> interpreter, so you can inspect it with the various tools available: >> >> * dir(obj) >> * help(obj) >> * type(obj).f # Will display <property object at 0x...> >> >> etc. Its hard to keep the existence of a property secret in Python. >> >> So once you know that f is a property, it might be hard to work out >> which of the fifty-seven superclasses and mixins it came from *wink* but >> that's neither here nor there :-) >> >> Maybe reporting "can't set property 'f'" is good enough. >> >> >> -- >> Steve >> _______________________________________________ >> Python-ideas mailing list -- python-ideas@python.org >> To unsubscribe send an email to python-ideas-le...@python.org >> https://mail.python.org/mailman3/lists/python-ideas.python.org/ >> Message archived at >> https://mail.python.org/archives/list/python-ideas@python.org/message/Z2AWWETWB72CKARR4DAHB3A2LFRLQR7X/ >> Code of Conduct: http://python.org/psf/codeofconduct/ >> >> -- >> >> --- >> You received this message because you are subscribed to a topic in the >> Google Groups "python-ideas" group. >> To unsubscribe from this topic, visit >> https://groups.google.com/d/topic/python-ideas/IMzPQhK64lw/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> python-ideas+unsubscr...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/python-ideas/20220211093720.GO16660%40ando.pearwood.info >> . >> > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/UW3D64ROFVSOEW6G6B3JTMB67ERRWW5D/ > Code of Conduct: http://python.org/psf/codeofconduct/ >
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