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Feature: reveal_type should work from comments #8864
Description
It would be great if reveal_type could be called from comments.
Mypy already looks at various comments to do its job, and reveal_type is not a runtime function, it only exists during a type check.
While experimenting with type hints in test code, I could write this:
a = some_func() # reveal_type(a)
Instead of:
a = some_func()
if typing.TYPE_CHECKING:
reveal_type(a)
Activity
JukkaL commentedon May 22, 2020
I'm not sure if this would be a net improvement. Now it's possible to comment out uses of
reveal_typeto temporarily silence them. What do others think?Also, this may be tricky to support since the parser we use drops most comments, I think.
ramalho commentedon May 22, 2020
Thanks for you response and your work on Mypy, @JukkaL.
The syntax for the comment can be different, to accommodate the current use of commenting out uses of
reveal_type, and make it easier for the parser. Maybe this:Before focusing on the syntax of the comment, what do people think of the idea of having a way to put calls to
reveal_typein test suites in a way that does not interfere with running the tests, and also doesn't require the cumbersomeif TYPE_CHECKINGguards?msullivan commentedon May 22, 2020
ramalho commentedon May 22, 2020
reveal_type()is a great debugging and learning feature.My use case is as a teacher and a writer: I have code that is tested with pytest, and is sprinkled with
reveal_typeto demonstrate Mypy's type inference. Perhaps havingif TYPE_CHECKINGguards is not too bad in normal Mypy usage, but in my examples it does add noise.I am biased, but I do believe that features that help with learning should be carefully considered, even if they don't seem useful to those with a lot of experience with the tool.
AlexWaygood commentedon Apr 1, 2022
@ramalho, does the recent addition of
typing.reveal_typeto the stdlib work for your use case? (It will be new in 3.11, but has also been added to thetyping_extensionsbackports package.)ramalho commentedon Apr 2, 2022
No, it does not solve my use case. Please consider my initial feature request and my responses to the other comments. Thanks!
JelleZijlstra commentedon Apr 2, 2022
The use case seems too marginal to justify the complexity, especially now that we have the runtime
reveal_type()available so you shouldn't needif TYPE_CHECKING:.ramalho commentedon Apr 3, 2022
I agree @JelleZijlstra. I did not know that
reveal_type()would no longer require theif. Thanks!