code: def sendall_stderr(self, s):
          
          while s:
              sent = self.send_stderr(s)
              s = s[sent:]
          return None
docs: Send data to the channel's "stderr" stream, without allowing partial
          results.  Unlike `send_stderr`, this method continues to send data
          from the given string until all data has been sent or an error occurs.
          Nothing is returned.
  
          :param str s: data to send to the client as "stderr" output.
  
          :raises socket.timeout:
              if sending stalled for longer than the timeout set by `settimeout`.
          :raises socket.error:
              if an error occurred before the entire string was sent.
  
          .. versionadded:: 1.1