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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:
 def download(self, attachment_id, destination):
 """ Download an attachment from Zendesk. :param attachment_id: id of the attachment to download :param destination: destination path. If a directory, the file will be placed in the directory with the filename from the Attachment object. :return: the path the file was written to """

        attachment = self(id=attachment_id)
        if os.path.isdir(destination):
            destination = os.path.join(destination, attachment.file_name)
        return self._download_file(attachment.content_url, destination)