试试下面:

try:
    raise ValueError("Original message. ")
except Exception as err:
    message = 'My custom error message. '
    # Change the order below to "(message + str(err),)" if custom message is needed first. 
    err.args = (str(err) + message,)
    raise 

输出:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
      1 try:
----> 2     raise ValueError("Original message")
      3 except Exception as err:
      4     message = 'My custom error message.'
      5     err.args = (str(err) + ". " + message,)

ValueError: Original message. My custom error message.

这个代码模板应该允许您用自定义消息引发异常。

try:
     raise ValueError
except ValueError as err:
    raise type(err)("my message")

如果你想自定义错误类型，你可以做的一件简单的事情就是基于ValueError定义一个错误类。

try:
    try:
        int('a')
    except ValueError as e:
        raise ValueError('There is a problem: {0}'.format(e))
except ValueError as err:
    print err

打印:

There is a problem: invalid literal for int() with base 10: 'a'

我尝试了这个精简版的@RobinL，效果很好:

try:
    do_something_that_might_raise_an_exception()
except ValueError as e:
    raise ValueError(f'Custom text {e}')

It seems all the answers are adding info to e.args[0], thereby altering the existing error message. Is there a downside to extending the args tuple instead? I think the possible upside is, you can leave the original error message alone for cases where parsing that string is needed; and you could add multiple elements to the tuple if your custom error handling produced several messages or error codes, for cases where the traceback would be parsed programmatically (like via a system monitoring tool).

## Approach #1, if the exception may not be derived from Exception and well-behaved:

def to_int(x):
    try:
        return int(x)
    except Exception as e:
        e.args = (e.args if e.args else tuple()) + ('Custom message',)
        raise

>>> to_int('12')
12

>>> to_int('12 monkeys')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in to_int
ValueError: ("invalid literal for int() with base 10: '12 monkeys'", 'Custom message')

or

## Approach #2, if the exception is always derived from Exception and well-behaved:

def to_int(x):
    try:
        return int(x)
    except Exception as e:
        e.args += ('Custom message',)
        raise

>>> to_int('12')
12

>>> to_int('12 monkeys')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in to_int
ValueError: ("invalid literal for int() with base 10: '12 monkeys'", 'Custom message')

你能看出这种方法的缺点吗?