'read a line from the file'

def readline(self):

    s = self.buffer_file.readline()
    if (s[(-1):] == '\n'):
        return s
    t = self.file.readline()
    if self._use_buffer:
        self.buffer_file.write(t)
        self._buffer_size += len(t)
    self._check_no_buffer()
    return (s + t)
