我想达到这样的效果:
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')
关于如何实现这一点，有什么线索吗?如何在Python 2和3中都做到这一点?
您可以定义从另一个异常继承的自己的异常，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)
假设你不想或不能修改foo()，你可以这样做:
try:
raise IOError('stuff')
except Exception as e:
if len(e.args) >= 1:
e.args = (e.args[0] + ' happens',) + e.args[1:]
raise
这确实是在Python 3中解决问题的唯一解决方案，而不会出现丑陋而令人困惑的“在处理上述异常期间，发生了另一个异常”消息。
如果要将重新提升的行添加到堆栈跟踪中，则应该写入raise e而不是raise。
我会这样做，这样在foo()中改变它的类型就不需要在bar()中也改变它。
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
这里有一个轻微的修改，保留了原始的回溯:
...
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。在2012-05-16对PEP 352的修改中(我的第一次更新发布于2012-03-12)，我的第一次更新中的代码在语法上是错误的，加上在BaseException上有消息属性的想法被撤销了。因此，目前在Python 3.5.2中，您需要按照这些行做一些事情来保留回溯，而不是在函数栏()中硬编码异常的类型。还要注意，会有这样一行:
During handling of the above exception, another exception occurred:
在显示的回溯消息中。
# 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同时在Python 2和3中工作。尽管由于语法差异，答案似乎是“否”，但有一种解决方法，即使用six外接组件模块中的rerraise()等帮助函数。因此，如果您出于某种原因不想使用这个库，下面是一个简化的独立版本。
还要注意，由于异常是在rerraise()函数中重新引发的，因此无论引发什么跟踪，都会出现异常，但最终结果是您想要的结果。
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')
我使用的一个方便的方法是使用类属性作为详细信息的存储，因为类属性可以从类对象和类实例中访问:
class CustomError(Exception):
def __init__(self, details: Dict):
self.details = details
然后在代码中:
raise CustomError({'data': 5})
当捕获错误时:
except CustomError as e:
# Do whatever you want with the exception instance
print(e.details)
与之前的答案不同，这适用于非常糟糕的__str__异常。 但是，它确实修改了类型，以便剔除无用的__str__实现。
我仍然希望找到一个不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')
原始的回溯和类型(名称)被保留。
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!
我将提供一段我经常使用的代码片段，每当我想向异常添加额外信息时。我在Python 2.7和3.6中都可以工作。
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))
上面的代码产生如下输出:
---------------------------------------------------------------------------
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例子有一点偏差，但我希望有人觉得它有用。
如果你来这里寻找Python 3的解决方案，手册上说:
当引发一个新的异常时(而不是使用一个简单的raise来重新引发当前正在处理的异常)，隐式异常上下文可以通过使用from和raise来补充显式原因:
raise new_exc from original_exc
例子:
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
最后是这样的:
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.
将一个完全无描述的TypeError转换为一个带有解决方案提示的漂亮消息，而不会搞乱原始异常。
到目前为止，我对所有给出的答案都不满意。他们还是太啰嗦了。在代码和消息输出中。
所有我想要的是stacktrace指向源异常，没有异常之间的东西，所以没有创建新的异常，只是重新提升原始与所有相关的堆栈帧状态在它，导致那里。
史蒂夫·霍华德给出了一个很好的答案，我想扩展一下，不，是简化一下……仅适用于python 3。
except Exception as e:
e.args = ("Some failure state", *e.args)
raise
唯一的新东西是参数展开/解包，这使得它对我来说足够小和容易使用。
试一试:
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
这将给你:
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'")
简单的漂亮图案可以是这样的
print("\n".join( "-"*i+" "+j for i,j in enumerate(e.args)))
这是我的实现，使用它作为上下文管理器，并可选地添加额外的消息异常:
from typing import Optional, Type
from types import TracebackType
class _addInfoOnException():
def __init__(self, info: str = ""):
self.info = info
def __enter__(self):
return
def __exit__(self,
exc_type: Optional[Type[BaseException]],
exc_val: BaseException, # Optional, but not None if exc_type is not None
exc_tb: TracebackType): # Optional, but not None if exc_type is not None
if exc_type:
if self.info:
newMsg = f"{self.info}\n\tLow level error: "
if len(exc_val.args) == 0:
exc_val.args = (self.info, )
elif len(exc_val.args) == 1:
exc_val.args = (f"{newMsg}{exc_val.args[0]}", )
elif len(exc_val.args) > 0:
exc_val.args = (f"{newMsg}{exc_val.args[0]}", exc_val.args[1:])
raise
用法:
def main():
try:
raise Exception("Example exception msg")
except Exception:
traceback.print_exc()
print("\n\n")
try:
with _addInfoOnException():
raise Exception("Example exception msg, no extra info")
except Exception:
traceback.print_exc()
print("\n\n")
try:
with _addInfoOnException("Some extra info!"):
raise Exception("Example exception msg")
except Exception:
traceback.print_exc()
print("\n\n")
if __name__ == "__main__":
main()
这将在这样的跟踪中解决:
Traceback (most recent call last):
File "<...>\VSCodeDevWorkspace\testis.py", line 40, in main
raise Exception("Example exception msg")
Exception: Example exception msg
Traceback (most recent call last):
File "<...>\VSCodeDevWorkspace\testis.py", line 47, in main
raise Exception("Example exception msg, no extra info")
File "<...>\VSCodeDevWorkspace\testis.py", line 47, in main
raise Exception("Example exception msg, no extra info")
Exception: Example exception msg, no extra info
Traceback (most recent call last):
File "<...>\VSCodeDevWorkspace\testis.py", line 54, in main
raise Exception("Example exception msg")
File "<...>\VSCodeDevWorkspace\testis.py", line 54, in main
raise Exception("Example exception msg")
Exception: Some extra info!
Low level error: Example exception msg
在PEP 678中，本机支持向异常添加注释:
try:
raise TypeError('bad type')
except Exception as e:
e.add_note('Add some information')
raise
呈现为:
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
TypeError: bad type
Add some information
我跳它可以取代史蒂夫霍华德的解决方案，不幸的是，它不给用户任何控制如何格式化最终的异常(例如，不能在异常之前添加一个注释，如:'错误在fn: {original_exc}')
如果想要对回溯进行更多控制，可以使用https://github.com/google/etils:
from etils import epy
with epy.maybe_reraise('Error in fn: '):
fn()
Or:
try:
fn()
except Exception as e:
epy.reraise(e, suffix='. Did you mean y ?')
以下是我在个人项目中使用的方法(我相信有足够的理由不在产品代码中这样做):
try:
#something hazardous
except Exception as e:
insightful_message = "shouldn't have done that"
amended_args = tuple([f'{e.args[0]}\n{insightful_message}', *e.args[1:]])
e.args = amended_args
raise
代码(1)拦截错误;(2)创建错误的.args属性的副本，这是一个元组，假定在索引0处包含一个错误消息，使用列表理解实现;(3)在错误消息后追加换行符和自定义消息;(4)使用。args附加到副本的任何附加项 拆包;(5)将副本转换为元组;最后(6)用修改后的副本替换。args。
这些操作大多是为了避免.args元组的不可变性。
我在代码中使用:
try:
a=1
b=0
c=a/b
except:
raise Exception(f"can't divide {a} with {b}")
输出:
---------------------------------------------------------------------------
ZeroDivisionError Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_11708/1469673756.py in <module>
3 b=0
----> 4 c=a/b
5
ZeroDivisionError: division by zero
During handling of the above exception, another exception occurred:
Exception Traceback (most recent call last)
~\AppData\Local\Temp/ipykernel_11708/1469673756.py in <module>
5
6 except Exception:
----> 7 raise Exception(f"can't divide {a} with {b}")
Exception: can't divide 1 with 0
