TypeError:描述符“lower”需要一个“str”对象，但收到一个“list”

Question

我现在用python编写代码，这是我的代码

tampa = []
for i in jawaban:
for j in jawaban[i]:
  lowertext = j.lower()
  lowertext = lowertext.translate(str.maketrans("","",string.punctuation))
  lowertext = re.sub("[^a-zA-Z0-9_]", " ",str(lowertext))
  #tokens = [a.split() for a in lowertext]
  tokens = word_tokenize(lowertext)
  stop_words = [line.rstrip('\n') for line in open('stopwordlist.txt')]
  filtered_text = [word for word in tokens if word not in stop_words]
  tampa.append(filtered_text)
factory = StemmerFactory()
stemmer = factory.create_stemmer()
stemmingA = []
for a in tampa:
  b   = stemmer.stem(a)
  stemming.append(b)
  a = " ".join(w for w in stemmingA)

我想预处理我的csv文件，但得到了TypeError：描述符“lower”需要一个“str”对象，但收到了一个“list”

你能帮我一下我的代码有什么问题吗（谢谢）