Wraps send(), sending string ``s`` to child process, with
        ``os.linesep`` automatically appended. Returns number of bytes
        written.  Only a limited number of bytes may be sent for each
        line in the default terminal mode, see docstring of :meth:`send`.

def sendline(self, s=''):
        '''Wraps send(), sending string ``s`` to child process, with
        ``os.linesep`` automatically appended. Returns number of bytes
        written.  Only a limited number of bytes may be sent for each
        line in the default terminal mode, see docstring of :meth:`send`.
        '''
        s = self._coerce_send_string(s)
        return self.send(s + self.linesep)