cython-cmake

This provides helpers for using Cython. Use:

find_package(Cython MODULE REQUIRED VERSION 3.0)
include(UseCython)

If you find Python beforehand, the search will take this into account. You can specify a version range on CMake 3.19+. This will define a Cython::Cython target (along with a matching CYTHON_EXECUTABLE variable). It will also provide the following helper function:

cython_transpile(<pyx_file>
                 [LANGUAGE C | CXX]
                 [CYTHON_ARGS <args> ...]
                 [OUTPUT <OutputFile>]
                 [OUTPUT_VARIABLE <OutputVariable>]
                 )

This function takes a pyx file and makes a matching .c / .cxx file in the current binary directory (exact path can be specified with OUTPUT). The location of the produced file is placed in the variable specified by OUTPUT_VARIABLE if given. Extra arguments to the Cython executable can be given with CYTHON_ARGS, and if this is not set, it will take a default from a CYTHON_ARGS variable.

If the LANGUAGE is not given, and both C and CXX are enabled globally, then the language will try to be deduced from a # distutils: language=... comment in the source file, and C will be used if not found.

This utility relies on the DEPFILE feature introduced for Ninja in CMake 3.7, and added for Make in CMake 3.20, and Visual Studio & Xcode in CMake 3.21.

Example

find_package(
  Python
  COMPONENTS Interpreter Development.Module
  REQUIRED)
find_package(Cython MODULE REQUIRED)

cython_transpile(simple.pyx LANGUAGE C OUTPUT_VARIABLE simple_c)

python_add_library(simple MODULE "${simple_c}" WITH_SOABI)

scikit-build-core

To use this package with scikit-build-core, you need to include it in your build requirements:

[build-system]
requires = ["scikit-build-core", "cython", "cython-cmake"]
build-backend = "scikit_build_core.build"

It is also recommended to require CMake 3.21:

[tool.scikit-build]
cmake.version = ">=3.21"

Vendoring

You can vendor FindCython and/or UseCython into your package, as well. This avoids requiring a dependency at build time and protects you against changes in this package, at the expense of requiring manual re-vendoring to get bugfixes and/or improvements. This mechanism is also ideal if you want to support direct builds, outside of scikit-build-core.

You should make a CMake helper directory, such as cmake. Add this to your CMakeLists.txt like this:

list(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake")

Then, you can vendor our files into that folder:

pipx run cython-cmake vendor cmake

If you want to just vendor one of the two files, use --member FindCython or --member UseCython. You can rerun this command to revendor. The directory must already exist.