'Load `self.line` with the `n`\'th next line and return it.'

def next_line(self, n=1):

    try:
        try:
            self.line_offset += n
            self.line = self.input_lines[self.line_offset]
        except IndexError:
            self.line = None
            raise EOFError
        return self.line
    finally:
        self.notify_observers()
