Building Python wheels with modern C++ standards (C++11 and later) requires a few tricks.
Python 2.7 and C++17¶
The Python 2.7 header files use the
register keyword, which is reserved and unused from C+17 onwards. Compiling a wheel for Python 2.7 with the C++17 standard is still possible to allow usage of
register using proper flag
-Wno-register for gcc/clang and
/wd5033 for MSVC.
manylinux1 and C++14¶
manylinux1 image (based on CentOS 5) contains a version of GCC and libstdc++ that only supports C++11 and earlier standards. There are however ways to compile wheels with the C++14 standard (and later): pypa/manylinux#118
manylinux2014 are newer and support all C++ standards (up to C++17).
macOS and deployment target versions¶
OS X/macOS allows you to specify a so-called "deployment target" version that will ensure backwards compatibility with older versions of macOS. One way to do this is by setting the
MACOSX_DEPLOYMENT_TARGET environment variable.
However, to enable modern C++ standards, the deploment target needs to be set high enough (since older OS X/macOS versions did not have the necessary modern C++ standard library).
To get C++11 and C++14 support,
MACOSX_DEPLOYMENT_TARGET needs to be set to (at least)
"10.9". By default,
cibuildwheel already does this, building 64-bit-only wheels for macOS 10.9 and later.
To get C++17 support, Xcode 9.3+ is needed, requiring at least macOS 10.13 on the build machine. To use C++17 library features and link against the C++ runtime library, set
"10.14" (or higher) - macOS 10.13 offers partial C++17 support (e.g., the filesystem header is in experimental, offering
#include <experimental/filesystem> instead of
#include <filesystem>); macOS 10.14 has full C++17 support.
However, if only C++17 compiler and standard template library (STL) features are used (not needing a C++17 runtime) it might be possible to set
MACOSX_DEPLOYMENT_TARGET to a lower value, such as
"10.9". To find out if this is the case, try compiling and running with a lower
MACOSX_DEPLOYMENT_TARGET: if C++17 features are used that require a more recent deployment target, building the wheel should fail.
For more details see https://en.cppreference.com/w/cpp/compiler_support, https://en.wikipedia.org/wiki/Xcode, and https://xcodereleases.com/: Xcode 10 needs macOS 10.13 and Xcode 11 needs macOS 10.14.
Windows and Python 2.7¶
Visual C++ for Python 2.7 does not support modern C++ standards (i.e., C++11 and later). When building on Appveyor, you will need to either use the "Visual Studio 2017" or "Visual Studio 2019" image, but Python 2.7 is not supported on these images - skip it by setting
There is an optional workaround for this, though: the pybind11 project argues and shows that it is possible to compile Python 2.7 extension with a newer compiler and has an example project showing how to do this: pybind/python_example. The main catch is that a user might need to install a newer "Microsoft Visual C++ Redistributable", since the newer C++ standard library's binaries are not included by default with the Python 2.7 installation.
setuptools to use a more recent version of MSVC that supports modern C++ can be done in the following way:
- Set the environment variables
MSSdk=1. These two environment variables will tell
setuptoolsto not search and set up a build environment that uses Visual C++ for Python 2.7 (aka. MSVC 9).
- Set up the build Visual Studio build environment you want to use, making sure that e.g.
- Usually, this can be done through
vcvarsall.bat x64. The exact location of this file depends on the installation, but the default path for VS 2019 Community (e.g. used in AppVeyor's
Visual Studio 2019image) is
C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat. Note:
vcvarsall.batchanges the environment variables, so this cannot be run in a subprocess/subshell and consequently running
CIBW_BEFORE_BUILDdoes not have any effect.
- In Azure Pipelines, a
VSBuildtask is available
- In GitHub Actions, the default shell is powershell, so you'll need to use
shell: cmdto source a
.batfile, and the directory is
"C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvarsall.bat". Or you can use an action, such as the
ilammy/msvc-dev-cmd@v1action to setup the environment (see example below).
- Usually, this can be done through
- Next, call
cibuildwheel. Unfortunately, MSVC has separate toolchains for compiling 32-bit and 64-bit, so you will need to run
cibuildwheeltwice: once with
CIBW_BUILD=*-win32after setting up the
x86build environment, and once with
x64environment (see previous step).
GitHub Action example with ilammy/msvc-dev-cmd:
- uses: ilammy/msvc-dev-cmd@v1 - name: Build 64-bit wheel run: python -m cibuildwheel --output-dir wheelhouse env: CIBW_BUILD: cp27-win_amd64 DISTUTILS_USE_SDK: 1 MSSdk: 1 - uses: ilammy/msvc-dev-cmd@v1 with: arch: x86 - name: Build 32-bit wheel run: python -m cibuildwheel --output-dir wheelhouse env: CIBW_BUILD: cp27-win32 DISTUTILS_USE_SDK: 1 MSSdk: 1