Python はリスト内で最も頻繁に出現する要素を検索します

>>> word_counter ={}
>>> for word in word_list:
  if word in word_counter:
    word_counter[word] +=1
  else:
    word_counter[word] = 1
>>> popular_word =sorted(word_counter, key = word_counter.get, reverse = True)
)
>>> top_3 = popular_word[:3]
>>> top_3
['is', 'OK', 'I']

>>> from collections import Counter
>>> c = Counter(word_list)
>>> c.most_common(3)

>>> counter ={}
>>> for i in word_list: counter[i] = counter.get(i, 0) + 1
>>> sorted([ (freq,word) for word, freq in counter.items() ], reverse=True)[:3]
[(4, 'is'), (3, 'OK'), (2, 'I')]