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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _build_robots_txt_checker(cls, session: AppSession):
        '''Build robots.txt checker.'''
        if session.args.robots:
            robots_txt_pool = session.factory.new('RobotsTxtPool')
            robots_txt_checker = session.factory.new(
                'RobotsTxtChecker',
                web_client=session.factory['WebClient'],
                robots_txt_pool=robots_txt_pool
            )

            return robots_txt_checker