The cppyy module is a frontend (see Package Structure), and most of the code is elsewhere. However, it does contain the docs for all of the modules, which are built using Sphinx: and published to using a webhook. To create the docs:

$ pip install sphinx_rtd_theme
Collecting sphinx_rtd_theme
Successfully installed sphinx-rtd-theme-0.2.4
$ cd docs
$ make html

The Python code in this module supports:

  • Interfacing to the correct backend for CPython or PyPy.
  • Pythonizations (TBD)


The cppyy-backend module contains two areas:

  • A patched copy of cling
  • Wrapper code

Package structure

There are four PyPA packages involved in a full installation, with the following structure:

              (A) _cppyy (PyPy)
          /                        \
(1) cppyy                            (3) cling-backend -- (4) cppyy-cling
          \                        /
            (2) CPyCppyy (CPython)

The user-facing package is always cppyy (1). It is used to select the other (versioned) required packages, based on the python interpreter for which it is being installed.

Below (1) follows a bifurcation based on interpreter. This is needed for functionality and performance: for CPython, there is the CPyCppyy package (2). It is written in C++, makes use of the Python C-API, and installs as a Python extension module. For PyPy, there is the builtin module _cppyy (A). This is not a PyPA package. It is written in RPython as it needs access to low-level pointers, JIT hints, and the _cffi_backend backend module (itself builtin).

Shared again across interpreters is the backend, which is split in a small wrapper (3) and a large package that contains Cling/LLVM (4). The former is still under development and expected to be updated frequently. It is small enough to download and build very quickly. The latter, however, takes a long time to build, but since it is very stable, splitting it off allows the creation of binary wheels that need updating only infrequently (expected about twice a year).

All code is publicly available; see the section on repositories.