如何修复错误异常以允许重试而不在 Python 中循环异常

Question

我正在尝试在 Python 2.7 中编写错误处理，以便在用户输入文件名后引发 IOError 异常。

我在互联网上尝试了几种解决方案，包括：

How to retry after exception? Get a Try statement to loop around until correct value obtained

这是我的原始代码：

while True: 
    try:
        with open (userFile, 'r') as txtFile:
            for curLine in txtFile:
                curLine = curLine.rstrip("\n\r")
                idList.append(curLine)
    except IOError:
        print("File does not exist")

每当引发 IOError 异常时，它都会进入一个无限循环，一遍又一遍地打印“文件不存在”。在我通过添加范围来限制尝试的情况下，它会通过该范围，一遍又一遍地打印，然后退出脚本。有谁知道为什么在引发异常时它会一直循环？

Answer 1

如果您将单独的关注点拆分为函数，这将容易得多，即 (i) 如果文件不存在则警告用户，以及 (ii) 将文件的内容读入行列表：

def read_file(f):
    # you can't read a file line-by-line and get line endings that match '\n\r'
    # the following will match what your code is trying to do, but perhaps not 
    # what you want to accomplish..?
    return f.read().split("\n\r")  # are you sure you haven't switched these..?

def checked_read_file(fname):
    try:
        with open(fname, 'rb') as fp:  # you'll probably need binary mode to read \r
            return read_file(fp)
    except IOError:
        print("File does not exist")
        return False

然后你可以编写你的while循环：

while True:
    result = checked_read_file(user_file)
    if result is not False:  # this is correct since the empty list is false-y
        break
    user_file = input("Enter another filename: ")  # or user_file = raw_input("...: ") if you're on Python 2

# here result is an array of lines from the file