“AttributeError：'NoneType'对象没有属性'readline'”的Python原因

Question

我正在尝试从每行有 1 个整数的文件中打印整数，并打印它们的总和。一切似乎都工作正常，除非我输入了错误的文件名，循环回来，然后输入正确的文件名。该程序仍然输出正确的信息，但随后出现错误： “AttributeError：‘NoneType’对象没有属性‘readline’”。为什么会这样？

def main():
    listnums = filetolist()
    print(f'numbers in file: {listnums}')
    print(f' sum of before mentioned numbers is: {sum(listnums)}')


# opens file
def openfile():
    try:
        file = open(input("what is the file named including the file extension?"), "r")
        return file
    except IOError:
        tryagain = input("File could not be found \n" + "if you would like try again type 1 and press enter, to exit press enter")
        if tryagain == "1":
            main()
        else:
            exit()


# converts file to list
def filetolist():
    file = openfile()
    line = file.readline()
    nums = []
    linenumber = 1
    while line != "":
        nums += [verifyint(line, linenumber)]
        line = file.readline()
        linenumber += 1
    file.close()
    return nums


# verifies number is an int
def verifyint(num, linenumber):
    try:
        numint = int(num)
        return numint
    except ValueError:
        print(f'Invalid value on line #{linenumber}')
        exit()


main()

Answer 1

当你点击except块时，没有return语句，所以这个函数在再次运行main()后返回None

您应该正确地引发错误并使用适当的循环，而不是有效地递归

def filetolist(filename):
    with open(filename) as f:
        return [int(line.rstrip()) for line in f]

def main():
    while True:
        filename = input("what is the file named including the file extension?")
        try:
            listnums = filetolist(filename)
            print(f'numbers in file: {listnums}')
            print(f' sum of before mentioned numbers is: {sum(listnums)}')
        except ValueError, IOError:
            again = input('Error! Try again? (y/n)')
            if again.lower() != 'y':
                break

main()

Answer 2

我认为（我可能错了）问题在于，当您无法读取文件并重试时，您需要调用openfile 而不是整个main。 如果您调用整个main，您将打开一个新文件，执行所有例程，然后什么也不返回。

试一试，告诉我它是否有效

def openfile():
    try:
        file = open(input("what is the file named including the file extension?"), "r")
        return file
    except IOError:
        tryagain = input("File could not be found \n" + "if you would like try again type 1 and press enter, to exit press enter")
        if tryagain == "1":
            return openfile()
        else:
            exit()

这里是截图