Fix a Callable type annotation.

[mzweilin]

What does this PR do?

Fixes #65

Type of change

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• [ ] Improvement (non-breaking)
• [x] Bug fix (non-breaking)
• [ ] New feature (non-breaking)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Testing

Please describe the tests that you ran to verify your changes. Consider listing any relevant details of your test configuration.

• [ ] Test A
• [ ] Test B

Before submitting

• [x] The title is self-explanatory and the description concisely explains the PR
• [x] My PR does only one thing, instead of bundling different changes together
• [ ] I list all the breaking changes introduced by this pull request
• [ ] I have commented my code
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] I have run pre-commit hooks with pre-commit run -a command without errors

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[mzweilin]

Running pytest -v locally (Python3.9.0) does catch the bug that is intentional in a01f346 (to be reverted later after we fix the test).

Python 3.9.15 (on other workstation) and 3.9.16 (on CI) tolerate the syntax error, that's why CI failed to catch it.

$ pytest -v
=========================================================================== test session starts ===========================================================================
platform linux -- Python 3.9.0, pytest-7.2.0, pluggy-1.0.0 -- /home/weilinxu/coder/MART/.venv/bin/python3.9
cachedir: .pytest_cache
rootdir: /home/weilinxu/coder/MART, configfile: pyproject.toml, testpaths: tests/
plugins: hydra-core-1.2.0, cov-4.0.0
collected 17 items / 16 errors                                                                                                                                            

================================================================================= ERRORS ==================================================================================
________________________________________________________________ ERROR collecting tests/test_adversary.py _________________________________________________________________
tests/test_adversary.py:13: in <module>
    import mart
mart/__init__.py:3: in <module>
    from mart import attack as attack
mart/attack/__init__.py:1: in <module>
    from .adversary import *
mart/attack/adversary.py:15: in <module>
    from .objective import Objective
mart/attack/objective/__init__.py:2: in <module>
    from .classification import *
mart/attack/objective/classification.py:25: in <module>
    class RandomTarget(Objective):
mart/attack/objective/classification.py:26: in RandomTarget
    def __init__(self, nb_classes: int, gain_fn: Callable[torch.Tensor, torch.Tensor]) -> None:
../../.pyenv/versions/3.9.0/lib/python3.9/typing.py:826: in __getitem__
    raise TypeError(f"Callable[args, result]: args must be a list."
E   TypeError: Callable[args, result]: args must be a list. Got <class 'torch.Tensor'>

[lumurillo]

I haven't been able to reproduce the issue. Can you provide more information about which conditions you got the issue? Which OS, Python version, etc.?

[mzweilin]

@lumurillo
Let's fix the syntax error first and try to improve testing later.