Installation

The cppyy module and its dependencies are available through PyPI for both CPython (2 and 3) and PyPy (5.9.0 and later). The cleanest/easiest way to install cppyy is using virtualenv and pip. However, if you do install with pip on Linux, it will select the manylinux1 binary wheels. Because the gcc compiler on manylinux1 is ancient (4.8.2), this will restrict you to C++11. Wheels also exist for Mac, where the chosen default is C++14.

For Mac and for Linux with a gcc that is newer than 7.2.0, manylinux1 wheels with C++17 enabled are available as well (they can’t live on PyPI, hence the external location). To use them, tell pip:

$ pip install --extra-index https://cern.ch/wlav/wheels cppyy

The alternative is to build from source. Build-time only dependencies are cmake (for general build), python (obviously, but also for LLVM), and a modern C++ compiler (one that supports at least C++11). By default, support for C++14 will be chosen. You can “upgrade” to C++17 or “downgrade” to C++11 by setting the STDCXX envar to ‘17’ or ‘11’ respectively when building, assuming your compiler supports it.

Compilation of the backend, which contains a customized version of Clang/LLVM, can take a long time, so by default the setup script will use all cores (x2 if hyperthreading is enabled). To change that behavior, set the MAKE_NPROCS environment variable to the desired number of processes to use. To see progress while waiting, use --verbose:

$ STDCXX=17 MAKE_NPROCS=32 pip install --verbose cppyy

The bdist_wheel of the backend is reused by pip for all versions of CPython and PyPy, thus the long compilation is needed only once. Unless you build on the manylinux1 docker images, wheels for cppyy-backend and for CPyCppyy are disabled, because setuptools (as used by pip) does not properly resolve dependencies for wheels. You will see a harmless error message to that effect fly by.

If you use the --user option to pip, make sure that the PATH envar points to the bin directory that will contain the installed entry points during the installation, as the build process needs them. You may also need to install wheel first. Example:

$ pip install wheel --user
$ PATH=$HOME/.local/bin:$PATH pip install cppyy --user

PyPy 5.7 and 5.8 have a built-in module cppyy. You can still install the cppyy package, but the built-in module takes precedence. To use cppyy, first import a compatibility module:

$ pypy
[PyPy 5.8.0 with GCC 5.4.0] on linux2
>>>> import cppyy_compat, cppyy
>>>>

You will have to set LD_LIBRARY_PATH appropriately if you get an EnvironmentError (it will indicate the needed directory).

Note that your python interpreter (whether CPython or pypy-c) may not have been linked by the C++ compiler. This can lead to problems during loading of C++ libraries and program shutdown. In that case, re-linking is highly recommended.

Older versions of PyPy (5.6.0 and earlier) have a built-in cppyy based on Reflex, which is less feature-rich and no longer supported. However, both the distribution tools and user-facing Python codes are very backwards compatible.