C++ API

The Doxygen generated C++ API reference can be found here

The following files and libraries are part of the PyNE C++ interface:

  • pyne
  • nucname
  • rxname
  • particle
  • data
  • material
  • enrichment
  • extra_types
  • h5wrap

Using the C++ API

While PyNE is a Python package, much of its core functionality exists purely in C/C++. The python wrappers that expose these C-level utilities exist independently of the the C-code. Therefore it is possible to use, compile, and link directly to PyNE core libraries from lower-level languages without having to touch Python at all. Additionally, this enables PyNE to be used from within other Python extension modules!

The API for PyNE functions on the C++ level is very similar to that which is exposed to Python. The differences lie largely in that C functions are strongly typed, whereas PyNE’s wrappers take heavy advantage of Python’s duck typing. For most use cases, the User’s Guide, the Python API, and the header files should be sufficient to describe the C++ API.

PyNE creates a single shared object called libpyne.so (or equivalent) and is installed into Python’s <prefix>/lib directory. The headers for C/C++ are installed into the <prefix>/include/pyne directory. Unfortunately, where <prefix> is located changes based on the Python interpreter and arguments passed to setup.py at install time. These often change from one system to another. However, these locations may be found from either the pyne or the pyne_config module.

In [1]: from pyne import lib, includes

In [2]: lib
Out[2]: '/usr/lib64'

In [3]: includes
Out[3]: '/usr/include'

Therefore to link against pyne, add the following options to your linker:

-lpyne -L$(python -c 'import pyne; print(pyne.lib)')

To include pyne from other C/C++ code, use the top-level pyne header:

#include "pyne/pyne.h"

And be sure that the include directory is on your C_INLCUDE_PATH and CPLUS_INLCUDE_PATH. You can do so from your compiler with:

-I$(python -c 'import pyne; print(pyne.includes)')

Amalgamating PyNE into a Single Source File

PyNE has a lot of great stuff in it! However, adding dependencies to C++ projects can be annoying, frustrating, and error prone. It often seems easier to just rip out the functionality that you need and include it in your own project.

Good news! PyNE offers a formal mechanism for combining some or all of its C++ API into a single, redistributable source file and an accompanying header file. This let’s you use pyne in your projects without adding pyne as an external dependency. This mechanism is known as amalgamation.

In the top level pyne source code directory, there is an amalgamate.py script. Simply run this script to combine all C++ source information into pyne.cpp and pyne.h files. Run with no options to combine all commonly used C++ files. Add options to modify the behavior. Current options are:

scopatz@ares ~/pyne $ ./amalgamate.py -h
usage: amalgamate.py [-h] [-s SOURCE_PATH] [-i HEADER_PATH]
                     [-f FILES [FILES ...]]

optional arguments:
  -h, --help            show this help message and exit
  -s SOURCE_PATH        Output *.cpp source path.
  -i HEADER_PATH        Output header path.
  -f FILES [FILES ...]  Files to amalgamate.

For example, to take only up through the rxname, amalgamate with:

scopatz@ares ~/pyne $ ./amalgamate.py -s pyne.cc -i pyne.h -f license.txt \
cpp/pyne.* cpp/extra_types.h cpp/h5wrap.h cpp/nucname.* cpp/rxname.*

Cyclus is an example of a project which uses an amalgamated version of pyne.