如何将捕获的异常(其描述和堆栈跟踪)转换为外部使用的str ?

try:
    method_that_can_raise_an_exception(params)
except Exception as e:
    print(complete_exception_description(e))

当前回答

在Python 3中,以下代码将格式化Exception对象,与使用traceback.format_exc()获得的结果完全相同:

import traceback

try: 
    method_that_can_raise_an_exception(params)
except Exception as ex:
    print(''.join(traceback.format_exception(etype=type(ex), value=ex, tb=ex.__traceback__)))

这样做的好处是只需要Exception对象(多亏了记录的__traceback__属性),因此可以更容易地将其作为参数传递给另一个函数进行进一步处理。

其他回答

对于使用Python-3的用户

使用回溯模块和异常。__traceback__可以提取堆栈跟踪,如下所示:

使用traceback.extract_stack()获取当前堆栈跟踪 删除最后三个元素(因为它们是堆栈中的条目,使我找到了调试函数) 使用traceback.extract_tb()从异常对象中追加__traceback__ 使用traceback.format_list()格式化整个内容

import traceback
def exception_to_string(excp):
   stack = traceback.extract_stack()[:-3] + traceback.extract_tb(excp.__traceback__)  # add limit=?? 
   pretty = traceback.format_list(stack)
   return ''.join(pretty) + '\n  {} {}'.format(excp.__class__,excp)

一个简单的演示:

def foo():
    try:
        something_invalid()
    except Exception as e:
        print(exception_to_string(e))

def bar():
    return foo()

当我们调用bar()时,我们得到以下输出:

  File "./test.py", line 57, in <module>
    bar()
  File "./test.py", line 55, in bar
    return foo()
  File "./test.py", line 50, in foo
    something_invalid()

  <class 'NameError'> name 'something_invalid' is not defined

如果你想将你的回溯转换为dict的列表(适用于python > 3.5):

from traceback import TracebackException


def list_traceback(exc_value: BaseException):
    result = list()

    # get previous fails, so errors are appended by order of execution
    if exc_value.__context__:
        result += list_traceback(exc_value.__context__)

    # convert Exception into TracebackException
    tbe = TracebackException.from_exception(exc_value)

    # get stacktrace (cascade methods calls)
    error_lines = list()
    for frame_summary in tbe.stack:
        summary_details = {
            'filename': frame_summary.filename,
            'method'  : frame_summary.name,
            'lineno'  : frame_summary.lineno,
            'code'    : frame_summary.line
        }
        error_lines.append(summary_details)

    # append error, by order of execution
    result.append({"error_lines": error_lines,
                   "type"       : tbe.exc_type.__name__,
                   "message"    : str(tbe)})

    return result

这将是结果(一个例子):

[
   {
      "error_lines": [
         {
            "filename": "/home/demo/file2.py",
            "method": "do_error_2",
            "lineno": 18,
            "code": "a=1/0"
         }
      ],
      "type": "ZeroDivisionError",
      "message": "division by zero"
   },
   {
      "error_lines": [
         {
            "filename": "/home/demo/file_main.py",
            "method": "demo2",
            "lineno": 50,
            "code": "file2.DEMO().do_error_2()"
         },
         {
            "filename": "/home/demo/file2.py",
            "method": "do_error_2",
            "lineno": 20,
            "code": "raise AssertionError(\"Raised inside the except, after division by zero\")"
         }
      ],
      "type": "AssertionError",
      "message": "Raised inside the except, after division by zero"
   }
]
>>> import sys
>>> import traceback
>>> try:
...   5 / 0
... except ZeroDivisionError as e:
...   type_, value_, traceback_ = sys.exc_info()
>>> traceback.format_tb(traceback_)
['  File "<stdin>", line 2, in <module>\n']
>>> value_
ZeroDivisionError('integer division or modulo by zero',)
>>> type_
<type 'exceptions.ZeroDivisionError'>
>>>
>>> 5 / 0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ZeroDivisionError: integer division or modulo by zero

您可以使用sys.exc_info()收集信息,并使用traceback模块中的函数对其进行格式化。 下面是一些格式化的例子。

整个异常字符串位于:

>>> ex = traceback.format_exception(type_, value_, traceback_)
>>> ex
['Traceback (most recent call last):\n', '  File "<stdin>", line 2, in <module>\n', 'ZeroDivisionError: integer division or modulo by zero\n']

您也可以考虑使用内置的Python模块cgitb,以获得一些非常好的、格式化良好的异常信息,包括局部变量值、源代码上下文、函数参数等。

例如这段代码…

import cgitb
cgitb.enable(format='text')

def func2(a, divisor):
    return a / divisor

def func1(a, b):
    c = b - 5
    return func2(a, c)

func1(1, 5)

我们得到这个异常输出…

ZeroDivisionError
Python 3.4.2: C:\tools\python\python.exe
Tue Sep 22 15:29:33 2015

A problem occurred in a Python script.  Here is the sequence of
function calls leading up to the error, in the order they occurred.

 c:\TEMP\cgittest2.py in <module>()
    7 def func1(a, b):
    8   c = b - 5
    9   return func2(a, c)
   10
   11 func1(1, 5)
func1 = <function func1>

 c:\TEMP\cgittest2.py in func1(a=1, b=5)
    7 def func1(a, b):
    8   c = b - 5
    9   return func2(a, c)
   10
   11 func1(1, 5)
global func2 = <function func2>
a = 1
c = 0

 c:\TEMP\cgittest2.py in func2(a=1, divisor=0)
    3
    4 def func2(a, divisor):
    5   return a / divisor
    6
    7 def func1(a, b):
a = 1
divisor = 0
ZeroDivisionError: division by zero
    __cause__ = None
    __class__ = <class 'ZeroDivisionError'>
    __context__ = None
    __delattr__ = <method-wrapper '__delattr__' of ZeroDivisionError object>
    __dict__ = {}
    __dir__ = <built-in method __dir__ of ZeroDivisionError object>
    __doc__ = 'Second argument to a division or modulo operation was zero.'
    __eq__ = <method-wrapper '__eq__' of ZeroDivisionError object>
    __format__ = <built-in method __format__ of ZeroDivisionError object>
    __ge__ = <method-wrapper '__ge__' of ZeroDivisionError object>
    __getattribute__ = <method-wrapper '__getattribute__' of ZeroDivisionError object>
    __gt__ = <method-wrapper '__gt__' of ZeroDivisionError object>
    __hash__ = <method-wrapper '__hash__' of ZeroDivisionError object>
    __init__ = <method-wrapper '__init__' of ZeroDivisionError object>
    __le__ = <method-wrapper '__le__' of ZeroDivisionError object>
    __lt__ = <method-wrapper '__lt__' of ZeroDivisionError object>
    __ne__ = <method-wrapper '__ne__' of ZeroDivisionError object>
    __new__ = <built-in method __new__ of type object>
    __reduce__ = <built-in method __reduce__ of ZeroDivisionError object>
    __reduce_ex__ = <built-in method __reduce_ex__ of ZeroDivisionError object>
    __repr__ = <method-wrapper '__repr__' of ZeroDivisionError object>
    __setattr__ = <method-wrapper '__setattr__' of ZeroDivisionError object>
    __setstate__ = <built-in method __setstate__ of ZeroDivisionError object>
    __sizeof__ = <built-in method __sizeof__ of ZeroDivisionError object>
    __str__ = <method-wrapper '__str__' of ZeroDivisionError object>
    __subclasshook__ = <built-in method __subclasshook__ of type object>
    __suppress_context__ = False
    __traceback__ = <traceback object>
    args = ('division by zero',)
    with_traceback = <built-in method with_traceback of ZeroDivisionError object>

The above is a description of an error in a Python program.  Here is
the original traceback:

Traceback (most recent call last):
  File "cgittest2.py", line 11, in <module>
    func1(1, 5)
  File "cgittest2.py", line 9, in func1
    return func2(a, c)
  File "cgittest2.py", line 5, in func2
    return a / divisor
ZeroDivisionError: division by zero

我定义了以下helper类:

import traceback
class TracedExeptions(object):
    def __init__(self):
        pass
    def __enter__(self):
        pass

    def __exit__(self, etype, value, tb):
      if value :
        if not hasattr(value, 'traceString'):
          value.traceString = "\n".join(traceback.format_exception(etype, value, tb))
        return False
      return True

我以后可以这样使用:

with TracedExeptions():
  #some-code-which-might-throw-any-exception

之后可以像这样消耗它:

def log_err(ex):
  if hasattr(ex, 'traceString'):
    print("ERROR:{}".format(ex.traceString));
  else:
    print("ERROR:{}".format(ex));

(背景:我很沮丧,因为使用承诺和异常一起,不幸的是将异常在一个地方引发到另一个地方的on_rejected处理程序,因此很难从原始位置获得回溯)