def METHOD_NAME(self):
    """Convert a single source file to a target format file."""
    for unit in self.source_store.units:
        key = unit.source
        if not key:
            continue
        target_unit = self.target_store.findid(key)
        if target_unit is None:
            target_unit = self.convert_unit(unit)
            self.target_store.addunit(target_unit)
        else:
            target_unit.target = unit.target