async def on_message_delta(self, delta: MessageDelta, snapshot: Message) -> None:
        """Callback that is fired whenever a message delta is returned from the API

        The first argument is just the delta as sent by the API and the second argument
        is the accumulated snapshot of the message. For example, a text content event may
        look like this:

        # delta
        MessageDeltaText(
            index=0,
            type='text',
            text=Text(
                value=' Jane'
            ),
        )
        # snapshot
        MessageContentText(
            index=0,
            type='text',
            text=Text(
                value='Certainly, Jane'
            ),
        )
        """
Callback that is fired whenever a message delta is returned from the API

        The first argument is just the delta as sent by the API and the second argument
        is the accumulated snapshot of the message. For example, a text content event may
        look like this:

        # delta
        MessageDeltaText(
            index=0,
            type='text',
            text=Text(
                value=' Jane'
            ),
        )
        # snapshot
        MessageContentText(
            index=0,
            type='text',
            text=Text(
                value='Certainly, Jane'
            ),
        )
        
src/openai/lib/streaming/_assistants.py