'Open an SFTP session to the remote host, and open a file on
that host.
:type filename: string
:param filename: The path to the file on the remote host.
:type mode: string
:param mode: The file interaction mode.
:type bufsize: integer
:param bufsize: The file buffer size.
:rtype: :class:`paramiko.sftp_file.SFTPFile`
:return: A paramiko proxy object for a file on the remote server.'

def open(self, filename, mode='r', bufsize=(-1)):

    sftp_client = self.open_sftp()
    return sftp_client.open(filename, mode, bufsize)
