如何正确使用 raise？答案

【问题标题】：How do I use raise correctly?如何正确使用 raise？
【发布时间】：2019-07-07 20:59:43
【问题描述】：

有人可以帮我在这段代码中获得某种结构吗？我是新来的。错误应捕获不存在的文件，以及不包含由“;”分隔的四部分行的文件。

程序应该如下所示：

测验文件的名称：hejsan
“导致输入/输出错误，请重试！”

测验文件的名称：namn.csv
“文件格式不正确。需要有四个字符串，用 ; 分隔在文件的每一行中。”

测验文件的名称：quiz.csv

quiz.csv 满足所有要求！

def get_quiz_list_handle_exceptions():
    success = True
    while success:
        try:

            file = input("Name of quiz-file: ")
            file2 = open(file,'r')

            for lines in range(0,9):
                quiz_line = file2.readline()
                quiz_line.split(";")

                if len(quiz_line) != 4:
                    raise Exception

    except FileNotFoundError as error:
        print("That resulted in an input/output error, please try again!", error)

    except Exception:
        print("The file is not on the proper format. There needs to be four strings, separated by ; in each line of the file.")

    else:
    success = False


get_quiz_list_handle_exceptions()

【问题讨论】：

Asking the user for input until they give a valid response 问题的答案可能会有所帮助。
您的except 子句缩进错误。将它们与try 对齐。 else 之后的语句也是如此。添加四个空格。

标签： python for-loop exception raise

【解决方案1】：

您的代码中存在缩进错误

def get_quiz_list_handle_exceptions():
success = True
while success:
    try:

        file = input("Name of quiz-file: ")
        file2 = open(file,'r')

        for lines in range(0,9):
            quiz_line = file2.readline()
            quiz_line.split(";")

            if len(quiz_line) != 4:
                raise Exception

    except FileNotFoundError as error:
        print("That resulted in an input/output error, please try again!", error)

    except Exception:
        print("The file is not on the proper format. There needs to be four strings, separated by ; in each line of the file.")
    else:
        success = False


get_quiz_list_handle_exceptions()

【讨论】：

【解决方案2】：

你有很多问题：

未能在多个位置正确缩进
未能保留split 的结果，因此您的长度测试是测试字符串的长度，而不是分号分隔的组件数
（次要）不使用 with 语句，也不关闭文件，因此文件句柄可能会无限期打开（取决于 Python 解释器）

固定代码：

def get_quiz_list_handle_exceptions():
    success = True
    while success:
        try:

            file = input("Name of quiz-file: ")
            with open(file,'r') as file2:  # Use with statement to guarantee file is closed
                for lines in range(0,9):
                    quiz_line = file2.readline()
                    quiz_line = quiz_line.split(";")

                    if len(quiz_line) != 4:
                        raise Exception

        # All your excepts/elses were insufficiently indented to match the try
        except FileNotFoundError as error:
            print("That resulted in an input/output error, please try again!", error)

        except Exception:
            print("The file is not on the proper format. There needs to be four strings, separated by ; in each line of the file.")
        else:
            success = False  # Fixed indent


get_quiz_list_handle_exceptions()

【讨论】：