PyHepMC is a collection of Python interfaces to HepMC event record objects.

New interface: hepmcio

The newer and more convenient interface is a minimal HepMC event file parser and set of Particle, Vertex, and Event objects, in the hepmcio Python module. This doesn't support all HepMC functionality, but enough for event structure investigations.


$ python >>> import hepmcio >>> reader = hepmcio.HepMCReader(INFILE) >>> evtnum = 0 >>> while True: >>> evtnum += 1 >>> evt = >>> if not evt: >>> break >>> print evtnum, evt.weights, len(evt.particles), len(evt.vertices)

This interface is used by the mcgraph2 event-graph plotter (which uses graphviz via the pydot module) and mcprint2 event summary printer scripts. You can adapt these for your own purposes.

Old interface: pyhepmc

The older interface uses the SWIG system ( to directly interface to the HepMC C++ library -- it currently needs some attention but in principle does everything that HepMC itself can do. To build this interface you'll need a copy of SWIG, the Python header files, and the HepMC library itself. To build it, specify the HepMC path on the command line: HEPMCPATH=/path/to/hepmc/installation python install --prefix=/install/to/here


$ python >>> import hepmc >>> io = hepmc.IO_GenEvent("LEP10.hepmc") >>> e = io.get_next_event()

Object ownership: the SWIG interface will automatically delete the C++ object when the Python proxy to it goes out of scope. If you don't want that, e.g. the C++ object will somehow clear up its own memory, then call e.g. myparticle.thisown = 0 to tell SWIG not to do any deletion of that object on the C++ side.