FAQs¶

This section covers common needs.

Starting a new project¶

The easiest way to get started is to use the Scientific Python cookie, which makes a new project following the Scientific Python Development Guidelines. Scikit-build-core is one of the backends you can select. The project will have a lot of tooling prepared for you as well, including pre-commit checks and a noxfile; be sure to read the guidelines to see what is there and how it works.

Another option is the pybind11 example.

In the future, a CLI interface with a new project generator is planned.

Multithreaded builds¶

For most generators, you can control the parallelization via a CMake define:

pip install -Ccmake.define.CMAKE_BUILD_PARALLEL_LEVEL=8 .

or an environment variable:

CMAKE_BUILD_PARALLEL_LEVEL=8 pip install .

The default generator on Unix-like platforms is Ninja, which automatically tries to run in parallel with the number of cores on your machine.

Dynamic setup.py options¶

While we will eventually have some dynamic options, most common needs can be moved into your CMakeLists.txt. For example, if you had a custom setup.py option (which setuptools has deprecated as well), you can make it a CMake option and then pass it with -Ccmake.define.<OPTION_NAME>=<value>. If you need to customize configuration options, try [[tool.scikit-build.overrides]]. If that is missing some value you need, please open an issue and let us know.

Finding Python¶

One common mistake when using FindPython is to forget to only request the Development.Module component. If you request Development, you will also require the Development.Embed component, which will require the Python libraries to be found for linking. When building a module on Unix, you do not link to Python - the Python symbols are already loaded in the interpreter. What’s more, the manylinux image (which is used to make redistributable Linux wheels) does not have the Python libraries, both to avoid this mistake, and to reduce size.

Cross compiling¶

When cross compiling, FindPython may not get the correct SOABI extension. Scikit-build-core does know the correct extension, however, and sets it as SKBUILD_SOABI. See the SOABI docs.

Things to try¶

If you want to debug a scikit-build-core build, you have several options. If you are using pip, make sure you are passing the -v flag, otherwise pip suppresses all output. You can increase scikit-build-core’s logging verbosity. You can also get a printout of the current settings using:

python -m scikit_build_core.builder

Repairing wheels¶

Like most other backends[1], scikit-build-core produced linux wheels, which are not redistrubutable cannot be uploaded to PyPI[2]. You have to run your wheels through auditwheel to make manylinux wheels. cibuildwheel automatically does this for you. See repairing.

Making a Conda recipe¶

scikit-build-core is available on conda-forge, and is used in dozens of recipes. There are a few things to keep in mind.

You need to recreate your build-system.requires in the host table, with the conda versions of your dependencies. You also need to add cmake and either make or ninja to your build: table. Conda-build hard-codes CMAKE_GENERATOR="Unix Makefiles on UNIX systems, so you have to set or unset this to use Ninja if you prefer Ninja. The scikit-build-core recipe cannot depend on cmake, make, or ninja, because that would add those to the wrong table (host instead of build). Here’s an example:

build:
  script:
   - {{ PYTHON }} -m pip install . -vv

requirements:
  build:
    - python                              # [build_platform != target_platform]
    - cross-python_{{ target_platform }}  # [build_platform != target_platform]
    - {{ compiler('c') }}
    - {{ stdlib('c') }}
    - {{ compiler('cxx') }}
    - cmake >=3.15
    - make                                 # [not win]
  host:
    - python
    - pip
    - scikit-build-core >=0.2.0
  run:
    - python

Supporting free-threaded builds on Windows¶

Windows currently requires a little extra care. You should set the C define Py_GIL_DISABLED on Windows; due to the way the two builds share the same config files, Python cannot set it for you on the free-threaded variant.