code: def __extend_targets_sources(target, source):
      
      if not SCons.Util.is_List(target):
          target = [target]
      if not source:
          source = target[:]
      elif not SCons.Util.is_List(source):
          source = [source]
      if len(target) < len(source):
          target.extend(source[len(target):])
          
      return target, source
docs: Prepare the lists of target and source files.