code: def sftp(self):
          
          if self._sftp is None:
              self._sftp = self.client.open_sftp()
          return self._sftp
docs: Return a `~paramiko.sftp_client.SFTPClient` object.
  
          If called more than one time, memoizes the first result; thus, any
          given `.Connection` instance will only ever have a single SFTP client,
          and state (such as that managed by
          `~paramiko.sftp_client.SFTPClient.chdir`) will be preserved.
  
          .. versionadded:: 2.0