什么是Python Key Error 2396，我该如何解决？

Question

# Import Libraries

from vaderSentiment.vaderSentiment import SentimentIntensityAnalyzer
import pandas as pd
import numpy as np

# Import the dataset as review
path = '/Users/kangh/OneDrive - University of Illinois - Urbana/Ricky/Study/School/UIUC Fall19/STAT 480/Group Project/reviews.csv'
review = pd.read_csv(path)
review = review[review['comments'].notnull()] # Remove the NAs
review.head()

The result of review.head()

# Sentiment analyzer

analyser = SentimentIntensityAnalyzer()

def sentiment_analyzer_scores(sentence):
    score = analyser.polarity_scores(sentence)
    print("{:-<40} {}".format(sentence, str(score)))

# Test the analyser
comments = review['comments']

sentiment_analyzer_scores(comments[0])

# Only output the compound score
analyser.polarity_scores(comments[350718]).get('compound')

# Distribution of compound score
def sentiment_arr(sentence):
    '''
    Only store the compound scroe of the comments
    '''
    ar = []
    for i in range(len(sentence)):
        score=analyser.polarity_scores(sentence[i]).get('compound')
        if np.isnan(score)==False:
            ar.append(score)
        else:
            ar.append(mean(ar))
    return ar

sentiment_arr(comments)

上面是我尝试的代码。 我的目的是将vadersentiment分析器（浮动）的结果存储到列表中。 在[sentiment_arr函数]中，得分是浮点数。

运行代码的最后一行后，出现如下错误：

---

Error of the result

错误原因是什么？我该怎么解决？