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?
当前回答
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 ?')
其他回答
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')
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。
也许
except Exception as e:
raise IOError(e.message + 'happens at %s'%arg1)
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
