def METHOD_NAME(self, directory):
    """
    Populate or update the force field from a directory.
    The provided directory must contain a subdirectory with the same name
    as the force field.
    """
    source_files = iter_force_field_files(directory)
    for source in source_files:
        extension = os.path.splitext(source)[-1]
        with open(source) as infile:
            FORCE_FIELD_PARSERS[extension](infile, self)