[Python-Dev] What should a good type checker do? (was: Please reject or postpone PEP 526) (original) (raw)

Stephen J. Turnbull turnbull.stephen.fw at u.tsukuba.ac.jp
Sat Sep 3 11:17:32 EDT 2016

Please respect Reply-To, set to python-ideas.

Greg Ewing writes:

Chris Angelico wrote:

Forcing people to write 1.0 just to be compatible with 1.5 will cause a lot of annoyance.

Indeed, this would be unacceptable IMO.

But "forcing" won't happen. Just ignore the warning. All such Python programs will continue to run (or crash) exactly as if the type declarations weren't there. If you don't like the warning, either don't run the typechecker, or change your code to placate it.

But allowing escapes from a typechecker means allowing escapes. All of them, not just the ones you or I have preapproved. I want my typechecker to be paranoid, and loud about it.

That doesn't mean I would never use a type like "Floatable" (ie, any type subject to implicit conversion to float). But in the original example, I would probably placate the typechecker. YMMV, of course.

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