Add example for NumPy and FindPython.

Author: hameerabbasi

projects/hello-numpy/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.18...3.22)
+
+project(hello-numpy VERSION "0.1")
+
+# Define CMAKE_INSTALL_xxx: LIBDIR, INCLUDEDIR
+include(GNUInstallDirs)
+include(FetchContent)
+
+find_package(Python COMPONENTS Development NumPy)
+
+set(python_module_name _hello)
+pybind11_add_module(${python_module_name} MODULE
+  src/hello/hello_py.cpp
+  )
+
+install(TARGETS ${python_module_name} DESTINATION .)
+
+# Quiet a warning, since this project is only valid with SKBUILD
+set(ignoreMe "${SKBUILD}")

projects/hello-numpy/README.md

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+# PyBind11 + Scikit Build example
+
+
+## Building
+
+To build, you must have pip 10 or greater, *or* you need to manually install
+`scikit-build` and `cmake`. Once you create a wheel, that wheel can be used in
+earlier versions of pip.
+
+Example build and install sequence:
+
+```bash
+pip install .
+python -c "import hello; hello.hello()"
+```
+
+This should print "Hello, World!".
+
+## Testing
+
+Testing is managed by tox. This will build the package in a temp directory and runs the tests in the test dir.
+
+```shell
+tox
+```

projects/hello-numpy/pyproject.toml

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+[build-system]
+requires = [
+    "setuptools",
+    "scikit-build>=0.15",
+    "cmake",
+    "ninja",
+    "numpy>=1.21",
+]
+build-backend = "setuptools.build_meta"
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]

projects/hello-numpy/setup.py

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+from skbuild import setup
+
+setup(
+    name="hello-numpy",
+    version="1.2.3",
+    description="a minimal example package (with pybind11 and NumPy)",
+    author='Hameer Abbasi',
+    license="MIT",
+    packages=['hello'],
+    package_dir={'': 'src'},
+    cmake_install_dir='src/hello',
+    python_requires='>=3.7',
+)

projects/hello-numpy/src/hello/__init__.py

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+from ._hello import hello, return_two
+
+
+__all__ = ("hello", "return_two")

projects/hello-numpy/src/hello/hello_py.cpp

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+#include <iostream>
+#include <pybind11/pybind11.h>
+#include <numpy/arrayobject.h>
+
+namespace py = pybind11;
+
+void hello() {
+    std::cout << "Hello, World!" << std::endl;
+}
+
+py::object zeros2x2() {
+    return py::reinterpret_steal<py::object>(
+        PyArray_ZEROS(2, {2, 2}, NPY_FLOAT64, 0);
+    );
+}
+
+PYBIND11_MODULE(_hello, m) {
+    m.doc() = "_hello";
+    m.def("hello", &hello, "Prints \"Hello, World!\"");
+    m.def("zeros2x2", &zeros2x2, "Returns a 2x2 array of zeros.");
+}

projects/hello-numpy/tests/test_hello_numpy.py

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+# This kind of import is automatically done when importing hello from outside
+import hello
+import unittest
+import numpy as np
+
+
+class TestHello(unittest.TestCase):
+    def test_hello(self):
+        hello.hello()
+
+    def test_return_two(self):
+        expected = np.zeros((2, 2), dtype=np.float64)
+        actual = hello.zeros2x2()
+        self.assertEqual(expected.dtype, actual.dtype)
+        self.assert_(np.all(expected == actual))
+
+
+if __name__ == "__main__":
+    unittest.main()
+    # You can run all python test with:
+    # ctest -R python -V
+    # from the build folder

projects/hello-numpy/tox.ini

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+[testenv]
+commands = python -m unittest discover -s tests/