Question

我想实现这样的目标：

def foo():
   try:
       raise IOError('Stuff ')
   except:
       raise

def bar(arg1):
    try:
       foo()
    except Exception as e:
       e.message = e.message + 'happens at %s' % arg1
       raise

bar('arg1')

Traceback...
  IOError('Stuff Happens at arg1')

但我得到的是：

Traceback..
  IOError('Stuff')

有关如何实现这一目标的任何线索？如何在Python 2和3中完成它？

Answer 1

我会这样做，因此在foo()中更改其类型也不需要在bar()中更改它。

def foo():
    try:
        raise IOError('Stuff')
    except:
        raise

def bar(arg1):
    try:
        foo()
    except Exception as e:
        raise type(e)(e.message + ' happens at %s' % arg1)

bar('arg1')

Traceback (most recent call last):
  File "test.py", line 13, in <module>
    bar('arg1')
  File "test.py", line 11, in bar
    raise type(e)(e.message + ' happens at %s' % arg1)
IOError: Stuff happens at arg1

更新1

这是一个略微修改，保留原始追溯：

...
def bar(arg1):
    try:
        foo()
    except Exception as e:
        import sys
        raise type(e), type(e)(e.message +
                               ' happens at %s' % arg1), sys.exc_info()[2]

bar('arg1')

Traceback (most recent call last):
  File "test.py", line 16, in <module>
    bar('arg1')
  File "test.py", line 11, in bar
    foo()
  File "test.py", line 5, in foo
    raise IOError('Stuff')
IOError: Stuff happens at arg1

更新2

对于Python 3.x，我的第一次更新中的代码在语法上是不正确的，加上message上BaseException属性的想法是retracted in a change to PEP 352在2012-05-16（我的第一次更新发布于2012-03-12）。所以目前，无论如何，在Python 3.5.2中，您需要沿着这些行做一些事情来保留回溯，而不是在函数bar()中硬编码异常类型。另请注意，将有一行：

During handling of the above exception, another exception occurred:

显示的追溯消息中的

。

# for Python 3.x
...
def bar(arg1):
    try:
        foo()
    except Exception as e:
        import sys
        raise type(e)(str(e) +
                      ' happens at %s' % arg1).with_traceback(sys.exc_info()[2])

bar('arg1')

更新3

一位评论者询问是否有一种方法可以在Python 2和3中使用。虽然由于语法差异，答案似乎是“否”，但是一种解决方法在reraise()附加模块中使用six之类的辅助函数。因此，如果您因某些原因而不想使用该库，则下面是简化的独立版本。

另请注意，由于异常在reraise()函数中重新启动，因此会出现任何回溯，但最终结果是您想要的。

import sys

if sys.version_info.major < 3:  # Python 2?
    # Using exec avoids a SyntaxError in Python 3.
    exec("""def reraise(exc_type, exc_value, exc_traceback=None):
                raise exc_type, exc_value, exc_traceback""")
else:
    def reraise(exc_type, exc_value, exc_traceback=None):
        if exc_value is None:
            exc_value = exc_type()
        if exc_value.__traceback__ is not exc_traceback:
            raise exc_value.with_traceback(exc_traceback)
        raise exc_value

def foo():
    try:
        raise IOError('Stuff')
    except:
        raise

def bar(arg1):
    try:
       foo()
    except Exception as e:
        reraise(type(e), type(e)(str(e) +
                                 ' happens at %s' % arg1), sys.exc_info()[2])

bar('arg1')

Answer 2

如果你来到这里寻找Python 3的解决方案the manual说：

在引发新异常时（而不是使用裸raise来重新引发当前正在处理的异常），可以通过使用from with raise来补充隐式异常上下文：

raise new_exc from original_exc

示例：

try:
    return [permission() for permission in self.permission_classes]
except TypeError as e:
    raise TypeError("Make sure your view's 'permission_classes' are iterable. "
                    "If you use '()' to generate a set with a single element "
                    "make sure that there is a comma behind the one (element,).") from e

最终看起来像这样：

2017-09-06 16:50:14,797 [ERROR] django.request: Internal Server Error: /v1/sendEmail/
Traceback (most recent call last):
File "venv/lib/python3.4/site-packages/rest_framework/views.py", line 275, in get_permissions
    return [permission() for permission in self.permission_classes]
TypeError: 'type' object is not iterable 

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
    # Traceback removed...
TypeError: Make sure your view's Permission_classes are iterable. If 
     you use parens () to generate a set with a single element make 
     sure that there is a (comma,) behind the one element.

将一个完全不起眼的TypeError变成一条带有提示解决方案的好消息，而不会弄乱原来的异常。

Answer 3

假设您不想或不能修改foo（），您可以这样做：

try:
    raise IOError('stuff')
except Exception as e:
    if len(e.args) >= 1:
        e.args = (e.args[0] + ' happens',) + e.args[1:]
    raise

这确实是解决Python 3中的问题的唯一解决方案，没有丑陋和混乱的问题＆＃34;在处理上述异常期间，发生了另一个异常＆＃34;消息。

如果应该将重新提升行添加到堆栈跟踪中，写raise e而不是raise就可以了。

Answer 4

我使用的一个方便的方法是使用class属性作为存储细节，因为class属性可以从类对象和类实例访问：

class CustomError(Exception):
    details = None

然后在你的代码中：

exc = CustomError('Some message')
exc.details('Details -- add whatever you want')
raise exc

当发现错误时：

except CustomError, e:
    # Do whatever you want with the exception instance
    print e
    print e.details

Answer 5

到目前为止，我不喜欢所有给出的答案。他们仍然太冗长，恕我直言。在代码和消息输出中。

我只想拥有指向源异常的stacktrace，在它们之间没有异常内容，因此不创建新的异常，只需在具有所有相关堆栈框架状态的情况下重新引发原始异常在其中，导致了那里。

Steve Howard给出了一个很好的答案，我想将其扩展为，不，仅将减少到python 3。

except Exception as e:
    e.args = ("Some failure state", *e.args)
    raise

唯一的新事物是parameter expansion/unpacking，它小巧易用。

尝试一下：

foo = None

try:
    try:
        state = "bar"
        foo.append(state)

    except Exception as e:
        e.args = ("Appending '"+state+"' failed", *e.args)
        raise

    print(foo[0]) # would raise too

except Exception as e:
    e.args = ("print(foo) failed: " + str(foo), *e.args)
    raise

这将为您提供：

Traceback (most recent call last):
  File "test.py", line 6, in <module>
    foo.append(state)
AttributeError: ('print(foo) failed: None', "Appending 'bar' failed", "'NoneType' object has no attribute 'append'")

简单的漂亮印刷可能类似于

print("\n".join( "-"*i+" "+j for i,j in enumerate(e.args)))

Answer 6

与以前的答案不同，这适用于非常糟糕__str__的异常。然而修改了类型，以便分解无用的__str__实现。

我仍然希望找到一个不会修改类型的额外改进。

from contextlib import contextmanager
@contextmanager
def helpful_info():
    try:
        yield
    except Exception as e:
        class CloneException(Exception): pass
        CloneException.__name__ = type(e).__name__
        CloneException.__module___ = type(e).__module__
        helpful_message = '%s\n\nhelpful info!' % e
        import sys
        raise CloneException, helpful_message, sys.exc_traceback


class BadException(Exception):
    def __str__(self):
        return 'wat.'

with helpful_info():
    raise BadException('fooooo')

保留原始追溯和类型（名称）。

Traceback (most recent call last):
  File "re_raise.py", line 20, in <module>
    raise BadException('fooooo')
  File "/usr/lib64/python2.6/contextlib.py", line 34, in __exit__
    self.gen.throw(type, value, traceback)
  File "re_raise.py", line 5, in helpful_info
    yield
  File "re_raise.py", line 20, in <module>
    raise BadException('fooooo')
__main__.BadException: wat.

helpful info!

Answer 7

我将提供一段代码，每当我想要向异常添加额外信息时，我经常使用这些代码。我在Python 2.7和3.6中都工作。

import sys
import traceback

try:
    a = 1
    b = 1j

    # The line below raises an exception because
    # we cannot compare int to complex.
    m = max(a, b)  

except Exception as ex:
    # I create my  informational message for debugging:
    msg = "a=%r, b=%r" % (a, b)

    # Gather the information from the original exception:
    exc_type, exc_value, exc_traceback = sys.exc_info()

    # Format the original exception for a nice printout:
    traceback_string = ''.join(traceback.format_exception(
        exc_type, exc_value, exc_traceback))

    # Re-raise a new exception of the same class as the original one, 
    # using my custom message and the original traceback:
    raise type(ex)("%s\n\nORIGINAL TRACEBACK:\n\n%s\n" % (msg, traceback_string))

上面的代码产生以下输出：

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-09b74752c60d> in <module>()
     14     raise type(ex)(
     15         "%s\n\nORIGINAL TRACEBACK:\n\n%s\n" %
---> 16         (msg, traceback_string))

TypeError: a=1, b=1j

ORIGINAL TRACEBACK:

Traceback (most recent call last):
  File "<ipython-input-6-09b74752c60d>", line 7, in <module>
    m = max(a, b)  # Cannot compare int to complex
TypeError: no ordering relation is defined for complex numbers

我知道这与问题中提供的示例略有不同，但我希望有人发现它有用。

Answer 8

您可以定义自己的继承自另一个的异常并创建它自己的构造函数来设置值。

例如：

class MyError(Exception):
   def __init__(self, value):
     self.value = value
     Exception.__init__(self)

   def __str__(self):
     return repr(self.value)

Answer 9

也许

except Exception as e:
    raise IOError(e.message + 'happens at %s'%arg1)

将信息添加到例外？

9 个答案: