我是mapreduce的新手，我正在努力寻找movielens 100k数据集中电影的平均影评。我有一个工作程序，可以找到每部电影的平均评论，但我只想对评论超过100的电影这样做。如何添加条件语句来执行此操作？

from mrjob.job import MRJob

class PopularMovieAvgReview(MRJob):
    def mapper(self, key, line):
        (userID, movieID, rating, timestamp) = line.split('\t')
        yield movieID, float(rating)

    def reducer(self, movieID, rating):
        total = 0
        numElements = 0 
        for x in rating:
            total += x
            numElements += 1
        yield movieID, total / numElements

if __name__ == '__main__':
    PopularMovieAvgReview.run()