Do not push partial types to the binder#20202
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JukkaL merged 2 commits intopython:masterfrom Nov 18, 2025
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
ilevkivskyi
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Nov 8, 2025
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I think this is correct, but I will give Jukka a chance to look at this as well.
JukkaL
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Nov 10, 2025
| if int(): | ||
| self.x = None | ||
| return | ||
| self.x = [""] |
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Also add a variant test case where the second assignment assigns a partial type as well -- e.g. self.x = [] followed by self.x.append('x').
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I tried this out, and it appears that the variant I proposed fails to infer the correct type even without using --allow-redefinition-new, so it's a pre-existing issue. I'll create an issue about it.
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Fixes #19996.
This was unearthed by #19400 where
is_subtype(Partial<X>, Partial<X>)started returning True - before thatbinder.assign_type(expr, Partial<None>, Partial<None>)just returned early. If I understand correctly, that is how Partial should be handled here: we do not want to push partials to the binder. I do not think we should add a special case for that (both False and True make some sense for a partial type, I am not convinced that either one is marginally better), so I just add an explicit guard to skip adding partial types here.