KeyError: 'this' , why this error happened?

Question

CORPUS = [
        'this is the first document',
        'this is the second document',
        'and this is the third document',
        'is this the first document ?'
    ]

doc = CORPUS
dic = {}
for sentence in doc:
  k = list(sentence.split())
  for term in k:
    count_term = k.count(term)
    if not dic[term]:
      dic[term] = count_term
    else:
      dic[term] += count_term
print(dic)

我想计算语料库列表中句子中术语的频率，所以我尝试制作字典并输入计数对象但KeyError：'this'

你能解释一下为什么会发生错误吗？

Answer 1

你应该改变条件：

if not dic[term] 到 if term not in dic

Answer 2

如果键不在字典中，它将抛出 KeyError，而不会 return None。您可以检查密钥是否在字典中

for term in k:
    count_term = k.count(term)
    if term not in dic:
        dic[term] = count_term
    else:
        dic[term] += count_term

或使用具有默认值的 get()，这将 return 0 以防键不在字典中

for term in k:
    count_term = k.count(term)
    dic[term] = dic.get(term, 0) + count_term

Answer 3

如果我理解正确，你的代码可以简化为：

from collections import Counter

print(Counter(" ".join(CORPUS).split()))

产生

Counter({'this': 4,
         'is': 4,
         'the': 4,
         'first': 2,
         'document': 4,
         'second': 1,
         'and': 1,
         'third': 1,
         '?': 1})

所以，我们的想法是首先创建一个避免循环的长字符串，然后使用内置函数来计算单个单词的出现次数。

您得到错误的原因在其他两个答案中得到了很好的解释（我对它们都投了赞成票）:)

KeyError: 'this' , why this error happened?

KeyError: 'this' , why this error happened?

python

keyerror