自定义异常处理显示错误消息和错误编号

Question

class My_custom_exception(Exception):
    def __init__(self, ErrNum, *arg, **kwargs):
        self.ErrNum = int(ErrNum)
        self.ErrMsg = ""  # Set appropriate message depending an error number

        if self.ErrNum  & 0x00000000 !=0:
            self.ErrMsg = "NO ERROR"
        if self.ErrNum   & 0x00000001 !=0:
            self.ErrMsg  = "Error 1 occured"
        if self.ErrNum   & 0x00000002 !=0:
            self.ErrMsg  = "Error 2 occured"
        if self.ErrNum   & 0x00000004 !=0:
            self.ErrMsg  = "Error 3 occured"
        if self.ErrNum   & 0x00000008 !=0:
            self.ErrMsg  = "Error 4 occured"

   def __str__(self):
        return "ERROR (0x%08X): %s" % (self.ErrNum, self.ErrMsg )

    def __repr__(self):
        return self.__str__()


def check_error(error_nr):
    if error_nr > 0:
        raise My_custom_exception(error_nr)

try:
    check_error(3)
except My_custom_exception as e:
    print e

输出：

My_custom_exception (0x00000003): Error 2 occurred.

我的目标是打印Error 1 occurred和Error 2 occurred

另一个问题是，如果我给出check_error(5)，那么Error 4 occurred，我也想避免这个问题

Answer 1

我会这样做：

class MyCustomException(Exception):  # note naming convention

    MESSAGES = {
        0x00000000: 'NO ERROR',
        0x00000001: 'Error 1 occurred',
        0x00000002: 'Error 2 occurred',
        0x00000004: 'Error 3 occurred',
        ...
    }

    def __init__(self, err_num, *args, **kwargs):
        super(MyCustomException, self).__init__(*args, **kwargs)  # handle inheritance
        self.err_num = int(err_num)
        self.err_msg = self._create_err_msg(self.err_num)

    def __str__(self):
        return "ERROR (0x%08X): %s" % (self.err_num, self.err_msg)

    def __repr__(self):
        # Note that __repr__ should be eval-able
        return 'MyCustomException(%d)' % self.err_num

    @classmethod
    def _create_err_msg(cls, err_num):
        messages = []
        for num, msg in cls.MESSAGES.items():
            if err_num & num:
                messages.append(msg)
        return ' and '.join(messages) if messages else cls.MESSAGES[0]

注意，通过将错误消息提取到dictionary类属性中，这简化了代码；将其作为一个单独的方法也可以更容易地进行单独测试：

>>> MyCustomException._create_err_msg(5)
'Error 1 occurred and Error 3 occurred'
>>> MyCustomException._create_err_msg(2)
'Error 2 occurred'
>>> MyCustomException._create_err_msg(0)
'NO ERROR'

使用中：

>>> exc = MyCustomException(5)
>>> str(exc)
'ERROR (0x00000005): Error 1 occurred and Error 3 occurred'