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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 get_attachment_data(cls, session, attachment_id):
 """Return a specific attachment's data. Args: session (requests.sessions.Session):
 Authenticated session. attachment_id (int):
 The ID of the attachment from which to get data. Returns: helpscout.models.AttachmentData: An attachment data singleton, if existing. Otherwise ``None``. """

        return cls(
            '/attachments/%d/data.json' % attachment_id,
            singleton=True,
            session=session,
            out_type=AttachmentData,
        )