我的代码中有这个try
块:
try:
do_something_that_might_raise_an_exception()
except ValueError as err:
errmsg = 'My custom error message.'
raise ValueError(errmsg)
严格来说,我实际上是在提出另一个ValueError
,而不是do_something...()
抛出的ValueError
,在这种情况下被称为err
。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,不可调用而失败:
try:
do_something_that_might_raise_an_exception()
except ValueError as err:
errmsg = 'My custom error message.'
raise err(errmsg)
足够幸运,只支持python 3.x,这真的变成了一件美丽的事情:)
从
我们可以使用 raise from 链接异常。
try:
1 / 0
except ZeroDivisionError as e:
raise Exception('Smelly socks') from e
在这种情况下,调用方将捕获的异常具有我们引发异常的位置的行号。
Traceback (most recent call last):
File "test.py", line 2, in <module>
1 / 0
ZeroDivisionError: division by zero
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "test.py", line 4, in <module>
raise Exception('Smelly socks') from e
Exception: Smelly socks
请注意,底部异常仅包含我们引发异常的堆栈跟踪。调用方仍可以通过访问他们捕获的异常的 __cause__
属性来获取原始异常。
with_traceback
或者您可以使用with_traceback。
try:
1 / 0
except ZeroDivisionError as e:
raise Exception('Smelly socks').with_traceback(e.__traceback__)
使用此表单,调用方将捕获的异常具有发生原始错误的位置的回溯。
Traceback (most recent call last):
File "test.py", line 2, in <module>
1 / 0
ZeroDivisionError: division by zero
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "test.py", line 4, in <module>
raise Exception('Smelly socks').with_traceback(e.__traceback__)
File "test.py", line 2, in <module>
1 / 0
Exception: Smelly socks
请注意,底部异常包含我们执行无效除法的行以及我们重新引发异常的行。
更新:对于 Python 3,请检查 Ben 的答案
2023 年更新:我十多年前写过这个答案,现在有更好的答案。你应该使用python 3和上面的答案。
原答案:
要将消息附加到当前异常并重新引发它,请执行以下操作:(外试/除外只是为了显示效果(
对于 python 2.x,其中 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
派生自ValueError
,这也将做正确的事情。例如UnicodeDecodeError
.
请注意,您可以添加任何您喜欢的内容err
。例如err.problematic_array=[1,2,3]
.
编辑:在评论中@Ducan点,上述内容不适用于python 3,因为.message
不是ValueError
的成员。相反,您可以使用这个(有效的python 2.6或更高版本或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))
编辑2:
根据目的,您还可以选择在自己的变量名称下添加额外的信息。对于 python2 和 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
这仅适用于Python 3。 您可以修改异常的原始参数并添加自己的参数。
异常会记住创建它的参数。 我认为这是为了您可以修改异常。
在函数reraise
中,我们在异常的原始参数前面加上我们想要的任何新参数(如消息(。 最后,我们在保留回溯历史记录的同时重新引发异常。
def reraise(e, *args):
'''re-raise an exception with extra arguments
:param e: The exception to reraise
:param args: Extra args to add to the exception
'''
# e.args is a tuple of arguments that the exception with instantiated with.
#
e.args = args + e.args
# Recreate the exception and preserve the traceback info so that we can see
# where this exception originated.
#
raise e.with_traceback(e.__traceback__)
def bad():
raise ValueError('bad')
def very():
try:
bad()
except Exception as e:
reraise(e, 'very')
def very_very():
try:
very()
except Exception as e:
reraise(e, 'very')
very_very()
输出
Traceback (most recent call last):
File "main.py", line 35, in <module>
very_very()
File "main.py", line 30, in very_very
reraise(e, 'very')
File "main.py", line 15, in reraise
raise e.with_traceback(e.__traceback__)
File "main.py", line 28, in very_very
very()
File "main.py", line 24, in very
reraise(e, 'very')
File "main.py", line 15, in reraise
raise e.with_traceback(e.__traceback__)
File "main.py", line 22, in very
bad()
File "main.py", line 18, in bad
raise ValueError('bad')
ValueError: ('very', 'very', 'bad')
似乎所有的答案都在向 e.args[0] 添加信息,从而改变现有的错误消息。 扩展参数元组是否有缺点? 我认为可能的好处是,对于需要解析该字符串的情况,您可以保留原始错误消息;如果自定义错误处理生成了多个消息或错误代码,则可以向元组添加多个元素,以便在以编程方式(例如通过系统监视工具(解析回溯的情况下。
## 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')
或
## 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')
你能看到这种方法的缺点吗?
Python 3.11+
PEP 678 – Enriching Exceptions with Notes 被接受并登陆 Python 3.11。新的 API 允许用户将自定义消息附加到现有错误。这对于在遇到错误时添加其他上下文非常有用。
使用add_note
方法适合回答原始问题:
try:
int("eleven")
except ValueError as e:
errmsg = "My custom error message."
e.add_note(errmsg)
raise
它将呈现如下:
Traceback (most recent call last):
File "/tmp/example.py", line 2, in <module>
int("eleven")
ValueError: invalid literal for int() with base 10: 'eleven'
My custom error message.
Python <3.11
修改 BaseException.__str__
用来呈现异常的 args
属性是唯一的方法。您可以扩展参数:
try:
int("eleven")
except ValueError as e:
errmsg = "My custom error message."
e.args += (errmsg,)
raise e
这将呈现为:
Traceback (most recent call last):
File "/tmp/example.py", line 2, in <module>
int("eleven")
ValueError: ("invalid literal for int() with base 10: 'eleven'", 'My custom error message.')
或者你可以替换args[0]
,这有点复杂,但会产生更干净的结果。
try:
int("eleven")
except ValueError as e:
errmsg = "My custom error message."
args = e.args
if not args:
arg0 = errmsg
else:
arg0 = f"{args[0]}n{errmsg}"
e.args = (arg0,) + args[1:]
raise
这将以与 Python 3.11+ 异常相同的方式呈现__notes__
:
Traceback (most recent call last):
File "/tmp/example.py", line 2, in <module>
int("eleven")
ValueError: invalid literal for int() with base 10: 'eleven'
My custom error message.
try:
try:
int('a')
except ValueError as e:
raise ValueError('There is a problem: {0}'.format(e))
except ValueError as err:
print err
指纹:
There is a problem: invalid literal for int() with base 10: 'a'
此代码模板应允许您使用自定义消息引发异常。
try:
raise ValueError
except ValueError as err:
raise type(err)("my message")
这是我用来修改 Python 2.7 和 3.x 中的异常消息的函数,同时保留原始回溯。它需要six
def reraise_modify(caught_exc, append_msg, prepend=False):
"""Append message to exception while preserving attributes.
Preserves exception class, and exception traceback.
Note:
This function needs to be called inside an except because
`sys.exc_info()` requires the exception context.
Args:
caught_exc(Exception): The caught exception object
append_msg(str): The message to append to the caught exception
prepend(bool): If True prepend the message to args instead of appending
Returns:
None
Side Effects:
Re-raises the exception with the preserved data / trace but
modified message
"""
ExceptClass = type(caught_exc)
# Keep old traceback
traceback = sys.exc_info()[2]
if not caught_exc.args:
# If no args, create our own tuple
arg_list = [append_msg]
else:
# Take the last arg
# If it is a string
# append your message.
# Otherwise append it to the
# arg list(Not as pretty)
arg_list = list(caught_exc.args[:-1])
last_arg = caught_exc.args[-1]
if isinstance(last_arg, str):
if prepend:
arg_list.append(append_msg + last_arg)
else:
arg_list.append(last_arg + append_msg)
else:
arg_list += [last_arg, append_msg]
caught_exc.args = tuple(arg_list)
six.reraise(ExceptClass,
caught_exc,
traceback)
使用
raise Exception('your error message')
或
raise ValueError('your error message')
在您想要引发它的地方或使用"from"将错误消息附加(替换(到当前异常中(仅支持 Python 3.x(:
except ValueError as e:
raise ValueError('your message') from e
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.
当前的答案对我不起作用,如果没有重新捕获异常,则不会显示附加的消息。
但是,在下面这样做既可以保留跟踪,也可以显示附加的消息,无论是否重新捕获异常。
try:
raise ValueError("Original message")
except ValueError as err:
t, v, tb = sys.exc_info()
raise t, ValueError(err.message + " Appended Info"), tb
(我用的是Python 2.7,没有在Python 3中尝试过(
Python 3 内置异常具有strerror
字段:
except ValueError as err:
err.strerror = "New error message"
raise err
上述解决方案都没有完全达到我想要的效果,即向错误消息的第一部分添加一些信息,即我希望我的用户首先看到我的自定义消息。
这对我有用:
exception_raised = False
try:
do_something_that_might_raise_an_exception()
except ValueError as e:
message = str(e)
exception_raised = True
if exception_raised:
message_to_prepend = "Custom text"
raise ValueError(message_to_prepend + message)
我尝试了这个紧凑版本的@RobinL,并且也工作:
try:
do_something_that_might_raise_an_exception()
except ValueError as e:
error_message = 'My error message'
raise ValueError(f'Custom text {error_message}')
引发相同的错误,前面有前缀自定义文本消息。(编辑 - 对不起,实际上和 https://stackoverflow.com/a/65494175/15229310 一样,为什么有 10 个(投票("解决方案"根本不回答发布的问题?
try:
<code causing exception>
except Exception as e:
e.args = (f"My custom text. Original Exception text: {'-'.join(e.args)}",)
raise
如果要自定义错误类型,您可以做的一件简单的事情就是基于 ValueError 定义一个错误类。