Get exception description and stack trace which caused an exception all as a string

Question

I ve seen a lot of posts about stack trace and exceptions in Python  But haven t found what I need   I have a chunk of Python 2 7 code that may raise an exception  I would like to catch it and assign to a string its full description and the stack trace that caused the error  simply all we use to see on the console   I need this string to print it to a text box in the GUI   Something like this   try      method that can raise an exception params  except Exception as e      print to textbox complete exception description e     The problem is  what is the function complete exception description

User · Answer

You might also consider using the built-in Python module, cgitb, to get some really good, nicely formatted exception information including local variable values, source code context, function parameters etc..

For instance for this code...

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)

we get this exception output...

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

User · Answer

gt  gt  gt  import sys  gt  gt  gt  import traceback  gt  gt  gt  try        5   0     except ZeroDivisionError as e        type   value   traceback    sys exc info    gt  gt  gt  traceback format tb traceback       File   lt stdin gt    line 2  in  lt module gt  n    gt  gt  gt  value  ZeroDivisionError  integer division or modulo by zero     gt  gt  gt  type   lt type  exceptions ZeroDivisionError  gt   gt  gt  gt   gt  gt  gt  5   0 Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  ZeroDivisionError  integer division or modulo by zero   You use sys exc info   to collect the information and the functions in the traceback module to format it  Here are some examples for formatting it   The whole exception string is at    gt  gt  gt  ex   traceback format exception type   value   traceback    gt  gt  gt  ex   Traceback  most recent call last   n      File   lt stdin gt    line 2  in  lt module gt  n    ZeroDivisionError  integer division or modulo by zero n

User · Answer

I defined following helper class   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   Which I can later use like this   with TracedExeptions       some-code-which-might-throw-any-exception   And later can consume it like this   def log err ex     if hasattr ex   traceString        print  ERROR     format ex traceString      else      print  ERROR     format ex       Background  I was frustraded because of using Promises together with Exceptions  which unfortunately passes exceptions raised in one place to a on rejected handler in another place  and thus it is difficult to get the traceback from original location

User · Answer

With Python 3  the following code will format an Exception object exactly as would be obtained using traceback format exc     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        The advantage being that only the Exception object is needed  thanks to the recorded   traceback   attribute   and can therefore be more easily passed as an argument to another function for further processing

User · Answer

my 2-cents   import sys  traceback try         except Exception  e    T  V  TB   sys exc info     print    join traceback format exception T V TB

User · Answer

For those using Python-3  Using traceback module and exception   traceback   one can extract the stack-trace as follows    grab the current stack-trace using traceback extract stack   remove the last three elements  as those are entries in the stack that got me to my debug function  append the   traceback   from the exception object using traceback extract tb   format the whole thing using traceback format list     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    A simple demonstration   def foo        try          something invalid       except Exception as e          print exception to string e    def bar        return foo     We get the following output when we call bar       File    test py   line 57  in  lt module gt      bar     File    test py   line 55  in bar     return foo     File    test py   line 50  in foo     something invalid       lt class  NameError  gt  name  something invalid  is not defined

User · Answer

Let s create a decently complicated stacktrace  in order to demonstrate that we get the full stacktrace   def raise error        raise RuntimeError  something bad happened     def do something that might error        raise error     Logging the full stacktrace  A best practice is to have a logger set up for your module  It will know the name of the module and be able to change levels  among other attributes  such as handlers   import logging logging basicConfig level logging DEBUG  logger   logging getLogger   name      And we can use this logger to get the error   try      do something that might error   except Exception as error      logger exception error    Which logs   ERROR   main   something bad happened  Traceback  most recent call last     File   lt stdin gt    line 2  in  lt module gt    File   lt stdin gt    line 2  in do something that might error   File   lt stdin gt    line 2  in raise error RuntimeError  something bad happened    And so we get the same output as when we have an error    gt  gt  gt  do something that might error   Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt    File   lt stdin gt    line 2  in do something that might error   File   lt stdin gt    line 2  in raise error RuntimeError  something bad happened    Getting just the string  If you really just want the string  use the traceback format exc function instead  demonstrating logging the string here   import traceback try      do something that might error   except Exception as error      just the string   traceback format exc       logger debug just the string    Which logs   DEBUG   main   Traceback  most recent call last     File   lt stdin gt    line 2  in  lt module gt    File   lt stdin gt    line 2  in do something that might error   File   lt stdin gt    line 2  in raise error RuntimeError  something bad happened

User · Answer

If you would like to get the same information given when an exception isn t handled you can do something like this  Do import traceback and then   try          except Exception as e      print traceback print tb e   traceback       I m using Python 3 7

User · Answer

See the traceback module  specifically the format exc   function  Here   import traceback  try      raise ValueError except ValueError      tb   traceback format exc   else      tb    No error  finally      print tb

User · Answer

If your goal is to make the exception and stacktrace message look exactly like when python throws an error  the following works in both python 2 3   import sys  traceback   def format stacktrace        parts     Traceback  most recent call last   n       parts extend traceback format stack limit 25   -2       parts extend traceback format exception  sys exc info    1        return    join parts     EXAMPLE BELOW     def a        b     def b        c     def c        d     def d        assert False   Noooh don t do it     print  THIS IS THE FORMATTED STRING   print                               n    try      a   except      stacktrace   format stacktrace       print stacktrace   print  THIS IS HOW PYTHON DOES IT   print                             n   a     It works by removing the last format stacktrace   call from the stack and joining the rest  When run  the example above gives the following output   THIS IS THE FORMATTED STRING                               Traceback  most recent call last     File  test py   line 31  in  lt module gt      a     File  test py   line 12  in a     b     File  test py   line 16  in b     c     File  test py   line 20  in c     d     File  test py   line 24  in d     assert False   Noooh don t do it   AssertionError  Noooh don t do it   THIS IS HOW PYTHON DOES IT                             Traceback  most recent call last     File  test py   line 38  in  lt module gt      a     File  test py   line 12  in a     b     File  test py   line 16  in b     c     File  test py   line 20  in c     d     File  test py   line 24  in d     assert False   Noooh don t do it   AssertionError  Noooh don t do it

User · Answer

For Python 3 5    So  you can get the stacktrace from your exception as from any other exception  Use traceback TracebackException for it  just replace ex with your exception    print    join traceback TracebackException from exception ex  format      An extended example and other features to do this   import traceback  try      1 0 except Exception as ex      print    join traceback TracebackException from exception ex  format       traceback format exc         join traceback format exception type ex   ex  ex   traceback        This is True        print    join traceback TracebackException from exception ex  format       The output will be something like this   True Traceback  most recent call last     File  untidsfsdfsdftled py   line 29  in  lt module gt      1 0 ZeroDivisionError  division by zero

[python] Get exception description and stack trace which caused an exception, all as a string

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