remove pybind usage, make example python agnostic

Author: janeyx99

extension_cpp/__init__.py

@@ -1,2 +1,10 @@
 import torch
-from . import _C, ops
+from pathlib import Path
+
+so_files = list(Path(__file__).parent.glob("_C*.so"))
+assert (
+    len(so_files) == 1
+), f"Expected one _C*.so file, found {len(so_files)}"
+torch.ops.load_library(so_files[0])
+
+from . import ops

extension_cpp/csrc/muladd.cpp

@@ -61,9 +61,6 @@ void myadd_out_cpu(const at::Tensor& a, const at::Tensor& b, at::Tensor& out) {
   }
 }
 
-// Registers _C as a Python extension module.
-PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {}
-
 // Defines the operators
 TORCH_LIBRARY(extension_cpp, m) {
   m.def("mymuladd(Tensor a, Tensor b, float c) -> Tensor");

setup.py

@@ -18,6 +18,11 @@
 
 library_name = "extension_cpp"
 
+if torch.__version__ >= "2.6.0":
+    py_limited_api = True
+else:
+    py_limited_api = False
+
 
 def get_extensions():
     debug_mode = os.getenv("DEBUG", "0") == "1"
@@ -59,6 +64,7 @@ def get_extensions():
             sources,
             extra_compile_args=extra_compile_args,
             extra_link_args=extra_link_args,
+            py_limited_api=py_limited_api,
         )
     ]
 
@@ -71,9 +77,10 @@ def get_extensions():
     packages=find_packages(),
     ext_modules=get_extensions(),
     install_requires=["torch"],
-    description="Example of PyTorch cpp and CUDA extensions",
+    description="Example of PyTorch C++ and CUDA extensions",
     long_description=open("README.md").read(),
     long_description_content_type="text/markdown",
     url="https://github.com/pytorch/extension-cpp",
     cmdclass={"build_ext": BuildExtension},
+    options={"bdist_wheel": {"py_limited_api": "cp39"}} if py_limited_api else {},
 )