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Utilities for building wheels that use third-party libraries

Update: Uploads, Rackspace, Anaconda

The original Multibuild default was to upload wheels to a Rackspace container, where Rackspace kindly donated the hosting to the Scikit-learn team. Rackspace finally stopped subsidizing this container. Some projects using Multibuild have moved to using https://anaconda.org/scientific-python-nightly-wheels, see SPEC04 for more info.

Introduction

A set of scripts to automate builds of macOS and manylinux wheels. It will work with windows, but that is not the prime target.

The CI scripts are designed to build and test:

  • 64-bit macOS x86_64 wheels built for macOS 10.9+
  • 64-bit macOS arm64 wheels built for macOS 10.6+
  • manylinux wheels in all the variations

You can build and test against all released versions of CPython and PyPy.

How does it work?

Multibuild is a series of bash scripts that define bash functions to build and test wheels.

Configuration is by overriding the default build function, and defining a test function.

The bash scripts are layered, in the sense that they are composed of a number of scripts which are sourced in sequence, each one potentially overriding previous ones.

macOS

The following bash scripts are sourced in this order:

multibuild/common_utils.sh
multibuild/osx_utils.sh
env_vars.sh
multibuild/configure_build.sh
multibuild/library_builders.sh
config.sh

See multibuild/travis_osx_steps.sh

The macOS build / test phases run on the VM started by CI. Therefore any environment variable defined in the CI script or the bash shell scripts listed above are available for your build and test.

Build options are controlled mainly by the following environment variables:

  • MB_PYTHON_VERSION sets the Python version targeted: major.minor.patch for CPython, or pypy-major.minor for PyPy.
  • MB_PYTHON_OSX_VER sets the minimum macOS SDK version for any C extensions. For CPython targets it may be set to 10.6, 10.9 or 11.0, provided a corresponding Python build is available at python.org. It defaults to the highest version available. It's ignored for PyPy targets.
  • PLAT sets the architectures built for any C extensions: x86_64 or arm64. It defaults to the same arches as the target Python version: arm64 for macOS 11.0; x86_64 for CPython macOS 10.9 or PyPy; and 64/32-bit for CPython 10.6.

In most cases it's best to rely on the defaults for MB_PYTHON_OSX_VER and PLAT, rather than setting them explicitly. Examples of exceptions to this guideline include:

  • setting MB_PYTHON_OSX_VER=10.6 to build a 10.6 CPython wheel for Python 2.7 (default for 2.7 is 10.9 64-bit)
  • setting MB_PYTHON_OSX_VER=10.6 and PLAT=x86_64 to build a 10.6 64-bit wheel.

The build_wheel function builds the wheel, and install_run function installs and tests it. Look in multibuild/common_utils.sh for default definitions of these functions. See below for more details, many of which are common to macOS and Linux.

Manylinux

The build phase is in a Manylinux Docker container, but the test phase is in a clean container.

Build phase

Specify the Manylinux version to build for with the MB_ML_VER environment variable. The default version is 2014. Versions that are currently valid are:

  • 1 corresponding to manylinux1 (see PEP 513).
  • 2010 corresponding to manylinux2010 (see PEP 571).
  • 2014 corresponding to manylinux2014 and adds more architectures to PLAT (see PEP 599).
  • _2_24 corresponding to manylinux_2_24 (see PEP 600).
  • _2_28 corresponding to manylinux_2_28 (see PEP 600).

The environment variable specified which Manylinux docker container you are building in.

The PLAT environment variable can be one of

  • x86_64, for 64-bit x86
  • i686, for 32-bit x86
  • s390x, for 64-bit s390x
  • ppc64le, for PowerPC
  • aarch64, for ARM
  • arm64, for Apple silicon
  • universal2, for both Apple silicon and 64-bit x86

The default is x86_64. Only x86_64 and i686 are valid on manylinux1 and manylinux2010.

multibuild/travis_linux_steps.sh defines the build_wheel function, which starts up the Manylinux1 Docker container to run a wrapper script multibuild/docker_build_wrap.sh, that (within the container) sources the following bash scripts:

multibuild/common_utils.sh
multibuild/manylinux_utils.sh
env_vars.sh
multibuild/configure_build.sh
multibuild/library_builders.sh
config.sh

See docker_build_wrap.sh to review the order of script sourcing.

See the definition of build_multilinux in multibuild/travis_linux_steps.sh for the environment variables passed from Travis CI to the Manylinux1 container.

Once in the container, after sourcing the scripts above, the wrapper runs the real build_wheel function, which now comes (by default) from multibuild/common_utils.sh.

Test phase

Specify the version to test with the DOCKER_TEST_IMAGE environment variable. The default version is dependent on MB_ML_LIBC and PLAT.

When MB_ML_LIBC is musllinux:

  • multibuild/alpine3.22_x86_64, when PLAT is x86_64
  • multibuild/alpine3.22_arm64v8, when PLAT is aarch64

Otherwise:

  • multibuild/noble_x86_64, when PLAT is x86_64
  • matthewbrett/trusty:32 when PLAT is i686 (Yes, an older image for 32-bit)
  • multibuild/noble_arm64v8 when PLAT is aarch64
  • multibuild/noble_ppc64le when PLAT is ppc64le
  • multibuild/noble_s390x when PLAT is s390x

Other valid values are any in https://quay.io/organization/pypa, using the correct platform code. Alternatively, you can use the substitution pattern multibuild/noble_{PLAT} in the .travis.yml file.

See multibuild/docker_test_wrap.sh.

multibuild/travis_linux_steps.sh defines the install_run function, which starts up the testing Docker container with the wrapper script multibuild/docker_test_wrap.sh. The wrapper script sources the following bash scripts:

multibuild/common_utils.sh
config.sh

See docker_test_wrap.sh for script source order.

See install_run in multibuild/travis_linux_steps.sh for the environment variables passed into the container.

It then (in the container) runs the real install_run command, which comes (by default) from multibuild/common_utils.sh.

Standard build and test functions

The standard build command is build_wheel. This is a bash function. By default the function that is run on macOS, and in the Manylinux container for the build phase, is defined in multibuild/common_utils.sh. You can override the default function in the project config.sh file (see below).

If you are building a wheel from PyPI, rather than from a source repository, you can use the build_index_wheel command, again defined in multibuild/common_utils.sh.

Typically, you can get away with leaving the default build_wheel / build_index_wheel functions to do their thing, but you may need to define a pre_build function in config.sh. The default build_wheel and build_index_wheel functions will call the pre_build function, if defined, before building the wheel, so pre_build is a good place to build any required libraries.

The standard test command is the bash function install_run. The version run on macOS and in the Linux testing container is also defined in multibuild/common_utils.sh. Typically, you do not override this function, but you in that case you will need to define a run_tests function, to run your tests, returning a non-zero error code for failure. The default install_run implementation calls the run_tests function, which you will likely define in config.sh. See the examples below for examples of less and more complicated builds, where the complicated builds override more of the default implementations.

To use these scripts

  • Make a repository for building wheels - e.g. https://github.com/MacPython/astropy-wheels - or in your case maybe https://github.com/your-org/your-project-wheels;

  • Add this (here) repository as a submodule:

    git submodule add https://github.com/multi-build/multibuild.git

  • Add your own project repository as another submodule:

    git submodule add https://github.com/your-org/your-project.git

  • For Travis CI, create a .travis.yml file, something like this:

    env:
    global:
        - REPO_DIR=your-project
        # Commit from your-project that you want to build
        - BUILD_COMMIT=v0.1.0
        # pip dependencies to _build_ your project
        - BUILD_DEPENDS="cython numpy"
        # pip dependencies to _test_ your project.  Include any dependencies
        # that you need, that are also specified in BUILD_DEPENDS, this will be
        # a separate install.
        # Now see the Uploads section for the stuff you need to
        # upload your wheels after CI has built them.

# You will likely prefer "language: generic" for travis configuration,
# rather than, say "language: python". Multibuild doesn't use
# Travis-provided Python but rather installs and uses its own, where the
# Python version is set from the MB_PYTHON_VERSION variable. You can still
# specify a language here if you need it for some unrelated logic and you
# can't use Multibuild-provided Python or other software present on a
# builder.
language: generic

# For CPython macOS builds only, the minimum supported macOS version and
# architectures of any C extensions in the wheel are set with the variable
# MB_PYTHON_OSX_VER: 10.9 (64-bit only) or 10.6 (64/32-bit dual arch). By
# default this is set to the highest available for the Python version selected
# using MB_PYTHON_VERSION. You should only need to set this explicitly if you
# are building a 10.6 dual-arch build for a CPython version where both a 10.9 and
# 10.6 build are available (for example, 2.7 or 3.7).
# All PyPy macOS builds are 64-bit only.

# Required in Linux to invoke `docker` ourselves
services: docker

# Host distribution.  This is the distribution from which we run the build
# and test containers, via docker.
dist: xenial

# osx image that enables building Apple silicon libraries
osx_image: xcode12.2

matrix:
  include:
    - os: linux
      env: MB_PYTHON_VERSION=2.7
    - os: linux
      env:
        - MB_PYTHON_VERSION=2.7
        - UNICODE_WIDTH=16
    - os: linux
      env:
        - MB_PYTHON_VERSION=2.7
        - PLAT=i686
    - os: linux
      env:
        - MB_PYTHON_VERSION=2.7
        - PLAT=i686
        - UNICODE_WIDTH=16
    - os: linux
      env:
        - MB_PYTHON_VERSION=3.5
    - os: linux
      env:
        - MB_PYTHON_VERSION=3.5
        - PLAT=i686
    - os: linux
      env:
        - MB_PYTHON_VERSION=3.6
    - os: linux
      env:
        - MB_PYTHON_VERSION=3.6
        - PLAT=i686
    - os: osx
      env:
        - MB_PYTHON_VERSION=2.7
        - MB_PYTHON_OSX_VER=10.6
    - os: osx
      env:
        - MB_PYTHON_VERSION=2.7
    - os: osx
      env:
        - MB_PYTHON_VERSION=3.5
    - os: osx
      env:
        - MB_PYTHON_VERSION=3.6
    - os: osx
      env:
        - MB_PYTHON_VERSION=3.7
        - MB_PYTHON_OSX_VER=10.6
    - os: osx
      env:
        - MB_PYTHON_VERSION=3.7
    - os: osx
      env:
        - MB_PYTHON_VERSION=3.8
    - os: osx
      env:
        - MB_PYTHON_VERSION=3.9
        - PLAT="universal2"
    - os: osx
      env:
        - MB_PYTHON_VERSION=3.9
    - os: osx
      language: generic
      env:
        - MB_PYTHON_VERSION=pypy-5.7

before_install:
    - source multibuild/common_utils.sh
    - source multibuild/travis_steps.sh
    - before_install

install:
    # Maybe get and clean and patch source
    - clean_code $REPO_DIR $BUILD_COMMIT
    - build_wheel $REPO_DIR $PLAT

script:
    - install_run $PLAT

after_success:
    # Here you should put the code to upload your wheels
    # See the Uploads section for more details.

    The example above is for a project building from a Git submodule. If you aren't building from a submodule, but want to use pip to build from a source archive on https://pypi.org or similar, replace the first few lines of the .travis.yml file with something like:

    env:
    global:
        # Instead of REPO_DIR, BUILD_COMMIT
        - PROJECT_SPEC="tornado==4.1.1"

    then your install section could look something like this:

    install:
    - build_index_wheel $PROJECT_SPEC

  • Next create a config.sh for your project, that fills in any steps you need to do before building the wheel (such as building required libraries). You also need this file to specify how to run your tests:

    # Define custom utilities
# Test for macOS with [ -n "$IS_MACOS" ]

function pre_build {
    # Any stuff that you need to do before you start building the wheels
    # Runs in the root directory of this repository.
    :
}

function run_tests {
    # Runs tests on installed distribution from an empty directory
    python --version
    python -c 'import sys; import yourpackage; sys.exit(yourpackage.test())'
}

    Optionally you can specify a different location for config.sh file with the $CONFIG_PATH environment variable.

  • Optionally, create an env_vars.sh file to override the defaults for any environment variables used by configure_build.sh/library_builders.sh. In Linux, the environment variables used for the build cannot be set in the .travis.yml file, because the build processing runs in a Docker container, so the only environment variables that reach the container are those passed in via the docker run command, or those set in env_vars.sh.

    As for the config.sh file, you can specify a different location for the file by setting the $ENV_VARS_PATH environment variable. The path in $ENV_VARS_PATH is relative to the repository root directory. For example, if your repository had a subdirectory scripts with a file my_env_vars.sh, you should set ENV_VARS_PATH=scripts/my_env_vars.sh.

  • Make sure your project is set up to build, and you should now be ready (to begin the long slow debugging process, probably).

  • For Apple silicon support you can either create an arm64 wheel or a universal2 wheel by supplying PLAT env variable. universal2 builds work on both arm64 and x86_64 platforms and also make it possible for the wheel code to work when switching the architecture on Apple silicon machines where x86_64 can be run using Rosetta2 emulation.

    There are two ways to build universal2 builds.

    1. Build with -arch x86_64 -arch arm64. These flags instruct the C/C++ compiler to compile twice and create a fat object/executable/library. This is the easiest, but has several drawbacks. If you are using C/C++ libraries that are built using library_builders, it's highly likely that they don't build correctly because most build systems and packages don't support building fat binaries. We could possibly build them separately and fuse them, but the headers might not be identical which is required when building the wheel as a universal2 wheel. If you are using Fortran, gfortran doesn't support fat binaries.
    2. Build arm64 and x86_64 wheels separately and fuse them. For this to work, we need to build the C/C++ libraries twice. Therefore, the library building is once called with BUILD_PREFIX=${BUILD_PREFIX:-/usr/local} for x86_64 and then called again with BUILD_PREFIX=/opt/arm64-builds. Once the two wheels are created, these two are merged. Both the arm64 and universal2 wheels are outputs for this build.

    In multibuild we are going with option 2. You can override this behaviour by overriding the function wrap_wheel_builder. To build Apple silicon builds, you should use a CI service with Xcode>=12 with universal build support and make sure that xcode is the default.

If your project depends on NumPy, you will want to build against the earliest NumPy that your project supports - see forward, backward NumPy compatibility. See the astropy-wheels Travis file for an example specifying NumPy build and test dependencies.

Here are some simple example projects:

Less simple projects where there are some serious build dependencies, and / or macOS / Linux differences:

Multibuild development

The main multibuild repository is always at https://github.com/multi-build/multibuild

We try to keep the master branch stable and do testing and development in the devel branch. From time to time we merge devel into master.

In practice, you can check out the newest commit from devel that works for you, then stay at it until you need newer features.

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Machinery for building and testing Python Wheels for Linux, OSX and (less flexibly) Windows.

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