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Respect sys.platform platform check assertion inside functions #9025
Description
This is a feature request
From the docs
https://mypy.readthedocs.io/en/stable/common_issues.html#python-version-and-system-platform-checks
More specifically, mypy will understand the use of sys.version_info and sys.platform checks
within if/elif/else statements.
and
As a special case, you can also use one of these checks in a top-level (unindented) assert; this makes mypy skip the rest of the file.
It would be nice if this kind of code would also typecheck on mac/linux.
Currently the option is to refactor such that you can define the entire function within an if sys.platform == "win32"
class A:
def func_on_win_only() -> str:
assert sys.platform == "win32"
return sys.getwindowsversion()
Activity
AlexWaygood commentedon Apr 4, 2022
I figured out a hacky workaround for this in #11909. Instead of having
assert sys.platform == "win32"at the top of the function, instead do this:ncoghlan commentedon Aug 27, 2024
Just noting that the
assert Falseform also works when filtering out single code branches within a larger function using a library or application specific check. For example:adam-grant-hendry commentedon Dec 8, 2024
Actually...this seems to break within
if/elsestatements too: gist, playgroundbrianschubert commentedon Dec 8, 2024
@adam-grant-hendry Mypy only supports testing
sys.platformusing basic equality checks. If you rewrite that assys.platform == 'win32' or sys.platform =='cygwin', it will work as expected.adam-grant-hendry commentedon Dec 8, 2024
Ah bummer…I kinda figured. Okay, I’ll just
#type: ignorethis one…switch platform test to work around mypy bugs
switch platform check to work around mypy bugs