如何使用Python中的自定义消息提升相同的异常？ [英] How do I raise the same Exception with a custom message in Python?

问题描述

我的代码中有 try block

I have this try block in my code:

try:
    do_something_that_might_raise_an_exception()
except ValueError as err:
    errmsg = 'My custom error message.'
    raise ValueError(errmsg)

严格来说，我其实是提高另一个 ValueError ，而不是 ValueError 由 do_something ...（）抛出，被称为 err 在这种情况下。如何将自定义消息附加到 err ？我尝试以下代码，但由于 err ，一个 ValueError 实例，而不是可调用：

Strictly speaking, I am actually raising another ValueError, not the ValueError thrown by do_something...(), which is referred to as err in this case. How do I attach a custom message to err? I try the following code but fails due to err, a ValueError instance, not being callable:

try:
    do_something_that_might_raise_an_exception()
except ValueError as err:
    errmsg = 'My custom error message.'
    raise err(errmsg)

推荐答案

更新：对于Python 3，请检查Ben的答案

附加消息到当前异常并重新提高它：
（外部尝试/除外仅仅是为了显示效果）

To attach a message to the current exception and re-raise it: (the outer try/except is just to show the effect)

对于python 2.x其中x > = 6：

For python 2.x where x>=6:

try:
    try:
      raise ValueError  # something bad...
    except ValueError as err:
      err.message=err.message+" hello"
      raise              # re-raise current exception
except ValueError as e:
    print(" got error of type "+ str(type(e))+" with message " +e.message)

如果 err 是从 ValueError 派生 。例如 UnicodeDecodeError 。

请注意，您可以将任何您喜欢的内容添加到 err 。例如 err.problematic_array = [1,2,3] 。

Note that you can add whatever you like to err. For example err.problematic_array=[1,2,3].

编辑： @Ducan指出上述内容不适用于python 3，因为 .message 不是<$ c的成员$ C> ValueError异常。相反，你可以使用这个（有效的python 2.6或更高版本或3.x）：

@Ducan points in a comment the above does not work with python 3 since .message is not a member of ValueError. Instead you could use this (valid python 2.6 or later or 3.x):

try:
    try:
      raise ValueError
    except ValueError as err:
       if not err.args: 
           err.args=('',)
       err.args = err.args + ("hello",)
       raise 
except ValueError as e:
    print(" error was "+ str(type(e))+str(e.args))

Edit2：

根据目的是什么，您还可以选择以您自己的变量名称添加额外的信息。对于python2和python3：

Depending on what the purpose is, you can also opt for adding the extra information under your own variable name. For both python2 and python3:

try:
    try:
      raise ValueError
    except ValueError as err:
       err.extra_info = "hello"
       raise 
except ValueError as e:
    print(" error was "+ str(type(e))+str(e))
    if 'extra_info' in dir(e):
       print e.extra_info

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