6. Making User Input Changes

Users are encouraged to use OpenMC’s Python API to build XML files that the OpenMC solver then reads during the initialization phase. Thus, to modify, add, or remove user input options, changes must be made both within the Python API and the C++ source that reads XML files produced by the Python API. The following steps should be followed to make changes to user input:

  1. Determine the Python class you need to change. For example, if you are adding a new setting, you probably want to change the openmc.Settings class. If you are adding a new surface type, you would need to create a subclass of openmc.Surface.

  2. To add a new option, the class will need a property attribute. For example, if you wanted to add a “fast_mode” setting, you would need two methods that look like:

    @property
    def fast_mode(self):
        ...
    
    @fast_mode.setter
    def fast_mode(self, fast_mode):
        ...
    
  3. Make sure that when an instance of the class is exported to XML (usually through a export_to_xml() or to_xml_element() method), a new element is written to the appropriate file. OpenMC uses the xml.etree.ElementTree API, so refer to the documentation of that module for guidance on creating elements/attributes.

  4. Make sure that your input can be categorized as one of the datatypes from XML Schema Part 2 and that parsing of the data appropriately reflects this. For example, for a boolean value, true can be represented either by “true” or by “1”.

  5. Now that you’re done with the Python side, you need to make modifications to the C++ codebase. Make appropriate changes in source files (e.g., settings.cpp). You should use convenience functions defined by xml_interface.cpp.

  6. If you’ve made changes in the geometry or materials, make sure they are written out to the statepoint or summary files and that the openmc.StatePoint and openmc.Summary classes read them in.

For most user input additions and changes, it is simple enough to follow a “monkey see, monkey do” approach. When in doubt, contact your nearest OpenMC developer or send a message to the developers mailing list.