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Fix joining of Sequence (e.g. variadic tuple) and fixed-length tuple #8335

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merged 1 commit into from Jan 31, 2020
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Fix joining of Sequence (e.g. variadic tuple) and fixed-length tuple #8335

merged 1 commit into from Jan 31, 2020

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intgr commented Jan 26, 2020 •
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For example:

  • Tuple[int] + Tuple[bool, ...] becomes Tuple[int, ...]
  • List[int] + Tuple[bool, ...] becomes Sequence[int]

This solves the other part of issue #4975 (along with PR #8333) and also issue #8074. Previously Mypy simply punted and returned object.

This was referenced Jan 26, 2020
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intgr requested a review from msullivan Jan 29, 2020
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JukkaL commented Jan 29, 2020

As discussed elsewhere, also testing subclasses of tuple would be a good idea.

intgr removed the request for review from msullivan Jan 29, 2020
intgr force-pushed the join-sequence-and-fixed-tuple branch from 5c552bb to 129cda7 Compare Jan 31, 2020
Fix joining of Sequence (e.g. variadic tuple) and fixed-length tuple
8bb19cf 
For example:
* Tuple[int] + Tuple[bool, ...] becomes Tuple[int, ...]
* List[int] + Tuple[bool, ...] becomes Sequence[int]

Previously Mypy simply punted and returned `object`.
intgr force-pushed the join-sequence-and-fixed-tuple branch from 129cda7 to 8bb19cf Compare Jan 31, 2020
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intgr commented Jan 31, 2020

I added test testTupleSubclassJoin, does that cover what you had in mind?

JukkaL approved these changes Jan 31, 2020
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JukkaL left a comment

Thanks, looks good! This is a nice type inference improvement.

JukkaL merged commit d640155 into python:master Jan 31, 2020
intgr mentioned this pull request Feb 2, 2020
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theodoretliu commented Feb 2, 2020

Quick question: why is subclassing "automatically" handled by this PR? This is more just for my curiosity, does the "default fallback" function automatically find the ancestor of the class?

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intgr commented Feb 2, 2020

@theodoretliu The tuple_fallback function returns a variadic tuple in place of a fixed-length tuple. But most tuple subclasses only support fixed-length operation, it cannot construct NamedTuple[int, ...] so it has to fall back to builtin.tuple class for tuple subclasses.

ethanhs mentioned this pull request Feb 3, 2020
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