原本是这样写的：df=pd.DataFrame(train_id,train_docid,train_question,train_answer)，就出现了错误，在变量外部加一个中括号写成

df=pd.DataFrame([train_id,train_docid,train_question,train_answer])就好了。train_id,train_docid,train_question,train_answer是4个字符串变量。