def _text_content(prompt: PromptMessage) -> str:

    if isinstance(prompt.content, str):

        return prompt.content

    content = prompt.content or []

    if any(item.type != PromptMessageContentType.TEXT for item in content):

        raise InvokeBadRequestError(

            f"{prompt.role.value} messages only support text content"

        )

    return "".join(cast(TextPromptMessageContent, item).data for item in content)