On Thu, Apr 22, 2021 at 4:11 AM Paul Moore <p.f.mo...@gmail.com> wrote:
> On Thu, 22 Apr 2021 at 11:21, Paul Moore <p.f.mo...@gmail.com> wrote: > > > > On Thu, 22 Apr 2021 at 11:06, Chris Angelico <ros...@gmail.com> wrote: > > > > > > Someone will likely correct me if this is inaccurate, but my > > > understanding is that that's exactly what you get if you just don't > > > give a type hint. The point of type hints is to give more information > > > to the type checker when it's unable to simply infer from usage and > > > context. > > > > Hmm, I sort of wondered about that as I wrote it. But in which case, > > what's the problem here? My understanding was that people were > > concerned that static typing was somehow in conflict with duck typing, > > but if the static checkers enforce the inferred duck type on untyped > > arguments, then that doesn't seem to be the case. Having said that, I > > thought that untyped arguments were treated as if they had a type of > > "Any", which means "don't type check". > > Looks like it doesn't: > > > cat .\test.py > def example(f) -> None: > f.close() > > import sys > example(12) > example(sys.stdin) > PS 12:00 00:00.009 C:\Work\Scratch\typing > > mypy .\test.py > Success: no issues found in 1 source file > > What I was after was something that gave an error on the first call, > but not on the second. Compare this: > > > cat .\test.py > from typing import Protocol > > class X(Protocol): > def close(self): ... > > def example(f: X) -> None: > f.close() > > import sys > example(12) > example(sys.stdin) > PS 12:03 00:00.015 C:\Work\Scratch\typing > > mypy .\test.py > test.py:10: error: Argument 1 to "example" has incompatible type > "int"; expected "X" > Found 1 error in 1 file (checked 1 source file) > Do note that this is only based on what mypy does, not necessarily what all Python type checkers do. I.e. it's quite possible pytype, pyre, or pyright infer more (especially https://pypi.org/project/pytype/ since they specifically say they infer types).
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