No error about repeated keyword argument

[denballakh]

Consider this code:

def f(**kwargs: object) -> None: ...
f(a=1, a=2) # no errors here

Expected Behavior
Error from mypy like this: SyntaxError: keyword argument repeated: a

Actual Behavior
At runtime:

  File "<some_file>", line 27
    f(a=1, a=2)
           ^^^
SyntaxError: keyword argument repeated: a

Mypy's output:

>mypy file.py
Success: no issues found in 1 source file

Your Environment

• Mypy version used: mypy 1.0.0+dev.154fee110f274fe6214eff856b65d437ee299fdb (compiled: no) (I did pip install -U git+https://github.com/python/mypy.git several minutes ago)
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: Python 3.11.0 (main, Oct 24 2022, 18:26:48) [MSC v.1933 64 bit (AMD64)] on win32

[A5rocks]

Weirdly enough, looks like mypy used to warn about this, but this error was removed between v0.812 and v0.902 (based on runs in mypy-play).

I'll go ahead and bisect! [will edit this]

[hauntsaninja]

@A5rocks if your bisection proves mysterious, I think there might be some Python version difference in whatever mypy-play.net is using

[A5rocks]

It does appear mysterious, I tried 53ec9f3 (very much before v0.812) and it passed without errors. I'm not sure the proper way to do this.

[hauntsaninja]

If I had to guess, it would be something like mypy-play.net is running 0.812 with Python 3.8 and 0.902 with Python 3.9. Or something like that

[JelleZijlstra]

Possibly relevant:

% ~/.pyenv/versions/3.8.16/bin/python -c 'import ast; ast.parse("f(a=1, a=2)")'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/jelle/.pyenv/versions/3.8.16/lib/python3.8/ast.py", line 47, in parse
    return compile(source, filename, mode, flags,
  File "<unknown>", line 1
SyntaxError: keyword argument repeated
% ~/.pyenv/versions/3.10.9/bin/python -c 'import ast; ast.parse("f(a=1, a=2)")'
%

[A5rocks]

That error does look like what mypy spit out! That would explain it, even if I can't on a cursory glance figure out where mypy-play would be overriding its default version of 3.10 (ymyzk/mypy-playground@c6d07eb)