Python mrjob -查找10个最长的单词，但mrjob返回重复的单词

from mrjob.job import MRJob
from mrjob.step import MRStep
import re

class WordCount(MRJob):

    def mapper(self, _, line):
        words = re.findall(r'\w+', line.lower())
        for word in words:
            yield len(word), word

    def reducer(self, length, words):
        top_10 = []
        for word in words:
            if word not in top_10:
                top_10.append(word)
                if len(top_10) > 10:
                    top_10.remove(min(top_10, key=len))
        for word in top_10:
            yield length, word

    def steps(self):
        return [
            MRStep(mapper=self.mapper, reducer=self.reducer)
        ]

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