python - 带有错误代码和错误消息的自定义 Python 异常

Question

class AppError(Exception):
    pass

class MissingInputError(AppError):
    pass

class ValidationError(AppError):
    pass

...

def validate(self):
    """ Validate Input and save it """

    params = self.__params

    if 'key' in params:
        self.__validateKey(escape(params['key'][0]))
    else:
        raise MissingInputError

    if 'svc' in params:
        self.__validateService(escape(params['svc'][0]))
    else:
        raise MissingInputError

    if 'dt' in params:
        self.__validateDate(escape(params['dt'][0]))
    else:
        raise MissingInputError


def __validateMulti(self, m):
    """ Validate Multiple Days Request"""

    if m not in Input.__validDays:
        raise ValidationError

    self.__dCast = int(m)

validate() 和 __validateMulti() 是验证和存储传递的输入参数的类的方法。从代码中可以看出，当某些输入参数丢失或某些验证失败时，我会引发一些自定义异常。

我想定义一些特定于我的应用的自定义错误代码和错误消息，例如，

Error 1100: "Key parameter not found. Please verify your input."

Error 1101: "Date parameter not found. Please verify your input"

...

Error 2100: "Multiple Day parameter is not valid. Accepted values are 2, 5 and 7."

并向用户报告。

1. 如何在自定义异常中定义这些错误代码和错误消息？
2. 如何以我知道要显示什么错误代码/消息的方式引发/捕获异常？

(PS:这是针对 Python 2.4.3)。

---

Bastien Léonard 在 SO comment 中提到你不需要总是定义一个新的 __init__ 或 __str__；默认情况下，参数将放在 self.args 中，并由 __str__ 打印。

因此，我更喜欢的解决方案:

class AppError(Exception): pass

class MissingInputError(AppError):
    
    # define the error codes & messages here
    em = {1101: "Some error here. Please verify.", \
          1102: "Another here. Please verify.", \
          1103: "One more here. Please verify.", \
          1104: "That was idiotic. Please verify."}

用法:

try:
    # do something here that calls
    # raise MissingInputError(1101)

except MissingInputError, e
    print "%d: %s" % (e.args[0], e.em[e.args[0]])

Answer 1

这是一个带有特殊代码的自定义 Exception 类的快速示例:

class ErrorWithCode(Exception):
    def __init__(self, code):
        self.code = code
    def __str__(self):
        return repr(self.code)

try:
    raise ErrorWithCode(1000)
except ErrorWithCode as e:
    print("Received error with code:", e.code)

既然您问的是如何使用 args，这里还有一个示例...

class ErrorWithArgs(Exception):
    def __init__(self, *args):
        # *args is used to get a list of the parameters passed in
        self.args = [a for a in args]

try:
    raise ErrorWithArgs(1, "text", "some more text")
except ErrorWithArgs as e:
    print("%d: %s - %s" % (e.args[0], e.args[1], e.args[2]))