def send_stderr(self, s):
m = Message()<EOL>m.add_byte(cMSG_CHANNEL_EXTENDED_DATA)<EOL>m.add_int(self.remote_chanid)<EOL>m.add_int(<NUM_LIT:1>)<EOL>return self._send(s, m)<EOL>
Send data to the channel on the "stderr" stream.  This is normally
only used by servers to send output from shell commands -- clients
won't use this.  Returns the number of bytes sent, or 0 if the channel
stream is closed.  Applications are responsible for checking that all
data has been sent: if only some of the data was transmitted, the
application needs to attempt delivery of the remaining data.

:param str s: data to send.
:return: number of bytes actually sent, as an `int`.

:raises socket.timeout:
    if no data could be sent before the timeout set by `settimeout`.

.. versionadded:: 1.1