def rename(self, oldpath, newpath):
return SFTP_OP_UNSUPPORTED<EOL>
Rename (or move) a file.  The SFTP specification implies that this
method can be used to move an existing file into a different folder,
and since there's no other (easy) way to move files via SFTP, it's
probably a good idea to implement "move" in this method too, even for
files that cross disk partition boundaries, if at all possible.

.. note:: You should return an error if a file with the same name as
    ``newpath`` already exists.  (The rename operation should be
    non-desctructive.)

.. note::
    This method implements 'standard' SFTP ``RENAME`` behavior; those
    seeking the OpenSSH "POSIX rename" extension behavior should use
    `posix_rename`.

:param str oldpath:
    the requested path (relative or absolute) of the existing file.
:param str newpath: the requested new path of the file.
:return: an SFTP error code `int` like ``SFTP_OK``.