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2.9. Handling LAMMPS errors

The shared library is compiled with C++ exception support to provide a better error handling experience. C++ exceptions allow capturing errors on the C++ side and rethrowing them on the Python side. This way LAMMPS errors can be handled through the Python exception handling mechanism.

from lammps import lammps, MPIAbortException

lmp = lammps()

try:
   # LAMMPS will normally terminate itself and the running process if an error
   # occurs. This would kill the Python interpreter. To avoid this, make sure to
   # compile with LAMMPS_EXCEPTIONS enabled. This ensures the library API calls
   # will not terminate the parent process. Instead, the library wrapper will
   # detect that an error has occured and throw a Python exception

   lmp.command('unknown')
except MPIAbortException as ae:
   # Single MPI process got killed. This would normally be handled by an MPI abort
   pass
except Exception as e:
   # All (MPI) processes have reached this error
   pass

Warning

Capturing a LAMMPS exception in Python can still mean that the current LAMMPS process is in an illegal state and must be terminated. It is advised to save your data and terminate the Python instance as quickly as possible when running in parallel with MPI.