def METHOD_NAME(self, ctx):
    properties = ctx.system_properties
    model_dir = properties.get("model_dir")
    source_vocab_path = os.path.join(model_dir, "source_vocab.pt")
    if os.path.isfile(source_vocab_path):
        return source_vocab_path
    else:
        raise Exception(
            "Missing the source_vocab file. Refer default handler "
            "documentation for details on using text_handler."
        )