python - 值错误 : I/O operation on closed (csv) file

Question

我收到这个错误:

Traceback (most recent call last):
  File "so.py", line 7, in <module>
    for review in x:
ValueError: I/O operation on closed file.

代码:

def get_reviews(path):
    with open(path, 'r', encoding = "utf-8") as file1:
        reviews = map(lambda x: x.strip().split(','), file1)
        return reviews

x = get_reviews("reviews.csv")
for review in x:
    print(review)

Answer 1

在 Python 3 中，map() 函数并不完全处理输入对象，而只是返回一个迭代器。因此，直到您的 for 循环调用每一行，文件才真正得到处理。但到那时，文件已经关闭，因为您的代码离开了 with block 。

这里有两个选择。首先，您可以让调用者传入一个打开的文件，并让他们处理打开和关闭文件:

def get_reviews(rev_file):
    return map(lambda x: x.strip().split(','), rev_file)

with open(path) as file1:
    for review in get_reviews(file1):
        print(review)

或者让 get_reviews() 完全处理文件，比如返回一个列表。

def get_reviews(path):
    with open(path, 'r', encoding = "utf-8") as file1:
        return list(map(lambda x: x.strip().split(','), file1))

# alternate version using a list comprehension instead of map()
def get_reviews(path):
    with open(path, 'r', encoding = "utf-8") as file1:
       return [x.strip().split(',') for x in file1]