change CastError to describe the isinstance failure
#5693
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LilyFirefly
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Dec 12, 2025
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LilyFirefly
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LilyFirefly
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The main change here looks good to me. I did spot a confusing test, but tidying that up isn't a blocker.
| assert_eq!( | ||
| err.to_string(), | ||
| "'NoneType' object cannot be cast as 'int | NoneType'" | ||
| "'NoneType' object is not an instance of 'int | NoneType'" |
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This test is weird. Is it important that we have NoneType twice, or would it be clearer to use, say, int | str? Because NoneType object (i.e. None) not being an instance of NoneType is at best very confusing, if not outright wrong.
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Hmm, good point. I wonder if in general we should consider special casing None in the error message too? e.g. 'None' is not an instance of instead of 'NoneType' object is not an instance of
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That sounds nice to have.
Tpt
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Dec 12, 2025
Icxolu
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Dec 13, 2025
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As discussed in #5472 (comment), this improves the clarity of the failure in
.cast()operations.cc @Icxolu @orlp