Fix: Remove misleading py_limited_api=cp39 wheel tag for PyTorch extension#1
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Description
This PR removes the
options={"bdist_wheel": {"py_limited_api": "cp39"}}argument fromhopper/setup.py.Why is this necessary?
Currently, the build system forces the generated wheels to be tagged as
cp39-abi3. While this implies the wheel is portable across Python 3.9+ environments, Flash Attention 3 is a PyTorch C++ extension.PyTorch C++ extensions are strictly linked to the PyTorch C++ ABI (e.g.,
libtorch_python.so), which changes between PyTorch versions.If a user compiles FA3 on Python 3.11 with PyTorch 2.11, the wheel is tagged
cp39-abi3. If they then attempt to install this wheel on a Python 3.9 environment (which requires an older PyTorch version since 2.11 dropped 3.9 support), the installation succeeds, but importing the module results in a fatal crash:ImportError: undefined symbol: aoti_torch_create_device_guardThe Fix
By removing the
py_limited_apioverride,setuptoolswill correctly tag the wheel with the exact CPython version it was built against (e.g.,cp311-cp311). This prevents users from sharing incompatible wheels across different Python/PyTorch environments and encountering silent ABI linker errors.