Add example of a project with an external c library and python bindings

projects/clib-wrapper/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.13.0)
+project(mylib LANGUAGES C)
+
+
+find_package(PythonInterp REQUIRED)
+find_package(PythonLibs REQUIRED)
+
+
+###
+# Private helper function to execute `python -c "<cmd>"`
+#
+# Runs a python command and populates an outvar with the result of stdout.
+# Be careful of indentation if `cmd` is multiline.
+#
+function(pycmd outvar cmd)
+  execute_process(
+    COMMAND "${PYTHON_EXECUTABLE}" -c "${cmd}"
+    RESULT_VARIABLE _exitcode
+    OUTPUT_VARIABLE _output)
+  if(NOT ${_exitcode} EQUAL 0)
+    message(ERROR "Failed when running python code: \"\"\"
+${cmd}\"\"\"")
+    message(FATAL_ERROR "Python command failed with error code: ${_exitcode}")
+  endif()
+  # Remove supurflous newlines (artifacts of print)
+  string(STRIP "${_output}" _output)
+  set(${outvar} "${_output}" PARENT_SCOPE)
+endfunction()
+
+###
+# Find scikit-build and include its cmake resource scripts
+#
+if (NOT SKBUILD)
+  pycmd(skbuild_location "import os, skbuild; print(os.path.dirname(skbuild.__file__))")
+  set(skbuild_cmake_dir "${skbuild_location}/resources/cmake")
+  # If skbuild is not the driver, then we need to include its utilities in our CMAKE_MODULE_PATH
+  list(APPEND CMAKE_MODULE_PATH ${skbuild_cmake_dir})
+endif()
+
+find_package(PythonExtensions REQUIRED)
+find_package(Cython REQUIRED)
+find_package(NumPy REQUIRED)
+
+
+# Backend C library
+add_subdirectory("src/cxx")
+
+# Cython library
+add_subdirectory("src/python/my_python_package")

projects/clib-wrapper/setup.py

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+"""
+Command to demonstrates the content of a built wheel
+
+..code::bash
+
+    python setup.py bdist_wheel
+    unzip -l dist/my_python_package-1.0.0-*.whl
+
+"""
+from skbuild import setup
+
+if __name__ == '__main__':
+    setup(
+        package_dir={'': 'src/python/'},
+        name="my_python_package",
+        version='1.0.0',
+        packages=['my_python_package'],
+    )

projects/clib-wrapper/src/cxx/CMakeLists.txt

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+set(MY_C_MODULE_NAME "my_c_module")
+
+list(APPEND sources "my_c_module.c")
+
+add_library(${MY_C_MODULE_NAME} SHARED ${sources})
+
+file(RELATIVE_PATH install_dest "${CMAKE_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}")
+install(TARGETS ${MY_C_MODULE_NAME} LIBRARY DESTINATION "${install_dest}")

projects/clib-wrapper/src/cxx/my_c_module.c

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+
+int my_c_func(int* int32_array, int num_items){
+    int result = 0;
+    for (int i = 0; i < num_items; i++){
+        result += int32_array[i];
+    }
+    return result;
+}

projects/clib-wrapper/src/cxx/my_c_module.h

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+#ifndef MYLIB_H
+#define MYLIB_H
+
+
+int my_c_func(int* int32_array, int num_items);
+
+
+#endif

projects/clib-wrapper/src/python/my_python_package/CMakeLists.txt

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+set(cython_source "_cython_wrapper.pyx")
+set(MODULE_NAME "_cython_wrapper")
+
+# Translate Cython into C/C++
+add_cython_target(${MODULE_NAME} "${cython_source}" C OUTPUT_VAR sources)
+
+# Add other C sources
+list(APPEND sources)
+
+# Create C++ library. Specify include dirs and link libs as normal
+add_library(${MODULE_NAME} MODULE ${sources})
+target_include_directories(
+  ${MODULE_NAME}
+  PUBLIC
+      ${NumPy_INCLUDE_DIRS}
+      ${PYTHON_INCLUDE_DIR}
+      ${CMAKE_CURRENT_SOURCE_DIR}
+)
+
+# TODO: not sure what the right way to do this is
+set(MY_C_MODULE_NAME "my_c_module")
+
+# What is the correct way to do this.
+target_link_libraries(${MODULE_NAME} ${MY_C_MODULE_NAME})
+
+target_compile_definitions(${MODULE_NAME} PUBLIC
+  "NPY_NO_DEPRECATED_API"
+  #"NPY_1_7_API_VERSION=0x00000007"
+  )
+
+python_extension_module(${MODULE_NAME})
+
+file(RELATIVE_PATH install_dest "${CMAKE_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}")
+install(TARGETS ${MODULE_NAME} LIBRARY DESTINATION "${install_dest}")

projects/clib-wrapper/src/python/my_python_package/__init__.py

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+from ._cython_wrapper import my_cython_func
+
+
+__all__ = ['my_cython_func']

projects/clib-wrapper/src/python/my_python_package/_cython_wrapper.pyx

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+cimport numpy as np
+
+
+cdef extern from "../../cxx/my_c_module.h":
+    cdef int my_c_func(int* int32_array, int num_items);
+
+
+def my_cython_func(np.ndarray[np.int32_t, ndim=1] int32_array):
+    """
+    Example:
+        >>> import numpy as np
+        >>> int32_array = np.arange(10) * 10
+        >>> result = my_cython_func(int32_array)
+        >>> print('result = {!r}'.format(result))
+    """
+
+    # Get a raw c view of the ndarray
+    cdef int [:] int32_array_view = int32_array
+    cdef int num_items = len(int32_array)
+
+    cdef int result = my_c_func(&int32_array_view[0], num_items)
+    return result

projects/clib-wrapper/test_script.sh

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+
+
+method1(){
+    # Build, view, install, and test the wheel
+    python setup.py bdist_wheel
+    unzip -l dist/my_python_package-1.0.0-*.whl
+
+    pip install dist/my_python_package-1.0.0-*.whl
+
+    pip uninstall my_python_package
+
+    python -c "import my_python_package"
+
+}