Change the "current directory" of this SFTP session.  Since SFTP
        doesn't really have the concept of a current working directory, this is
        emulated by Paramiko.  Once you use this method to set a working
        directory, all operations on this `.SFTPClient` object will be relative
        to that path. You can pass in ``None`` to stop using a current working
        directory.

        :param str path: new current working directory

        :raises IOError: if the requested path doesn't exist on the server

        .. versionadded:: 1.4

def chdir(self, path=None):
        """
        Change the "current directory" of this SFTP session.  Since SFTP
        doesn't really have the concept of a current working directory, this is
        emulated by Paramiko.  Once you use this method to set a working
        directory, all operations on this `.SFTPClient` object will be relative
        to that path. You can pass in ``None`` to stop using a current working
        directory.

        :param str path: new current working directory

        :raises IOError: if the requested path doesn't exist on the server

        .. versionadded:: 1.4
        """
        if path is None:
            self._cwd = None
            return
        if not stat.S_ISDIR(self.stat(path).st_mode):
            raise SFTPError(errno.ENOTDIR, "%s: %s" % (os.strerror(errno.ENOTDIR), path))
        self._cwd = b(self.normalize(path))