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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 async def attach_url(self, url: str, description: str = None) -> Attachment: """ add an url as an attachment |methcoro| Args: url: url you want to add description: *optional* description for your attachment Returns: Attachment: Raises: ValueError: url must not be None APIException """

        return await self._attach(url=url, description=description)