Message416817
Thanks for your report, but I would appreciate a more concise explanation. Let me try to rephrase the problem.
Given this function:
def mean(x: list[float]) -> float:
return sum(x) / len(x)
We want to provide a guarantee that if x is a nonempty list containing only floats, the function returns successfully and returns a float.
But the type system currently doesn't give this guarantee, because PEP 484 specifies that ints are compatible with floats, and `mean([0.0, 1.25, 10**1000, 0.0])` will throw OverflowError.
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We generally discuss issues with the general type system over at https://github.com/python/typing/issues, but here are a few thoughts:
- The type system doesn't generally try to cover exceptions. Your function could also raise MemoryError, or KeyboardInterrupt, and the type system can't tell you.
- The concrete proposal here would be to make int no longer implicitly compatible with float. That might be nice, but at this point it would be a big break in backwards compatibility, so I'm not sure we can do it. |
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Date |
User |
Action |
Args |
2022-04-05 20:52:43 | JelleZijlstra | set | recipients:
+ JelleZijlstra, gvanrossum, kj, AlexWaygood, tfish2 |
2022-04-05 20:52:43 | JelleZijlstra | set | messageid: <1649191963.06.0.307787776087.issue47234@roundup.psfhosted.org> |
2022-04-05 20:52:43 | JelleZijlstra | link | issue47234 messages |
2022-04-05 20:52:42 | JelleZijlstra | create | |
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