traceback.format_exc() will yield more info if that's what you want.
import traceback
def do_stuff():
raise Exception("test exception")
try:
do_stuff()
except Exception:
print(traceback.format_exc())
This outputs:
Traceback (most recent call last):
File "main.py", line 9, in <module>
do_stuff()
File "main.py", line 5, in do_stuff
raise Exception("test exception")
Exception: test exception
traceback.format_exc() will yield more info if that's what you want.
import traceback
def do_stuff():
raise Exception("test exception")
try:
do_stuff()
except Exception:
print(traceback.format_exc())
This outputs:
Traceback (most recent call last):
File "main.py", line 9, in <module>
do_stuff()
File "main.py", line 5, in do_stuff
raise Exception("test exception")
Exception: test exception
Some other answer have already pointed out the traceback module.
Please notice that with print_exc, in some corner cases, you will not obtain what you would expect. In Python 2.x:
import traceback
try:
raise TypeError("Oups!")
except Exception, err:
try:
raise TypeError("Again !?!")
except:
pass
traceback.print_exc()
...will display the traceback of the last exception:
Traceback (most recent call last):
File "e.py", line 7, in <module>
raise TypeError("Again !?!")
TypeError: Again !?!
If you really need to access the original traceback one solution is to cache the exception infos as returned from exc_info in a local variable and display it using print_exception:
import traceback
import sys
try:
raise TypeError("Oups!")
except Exception, err:
try:
exc_info = sys.exc_info()
# do you usefull stuff here
# (potentially raising an exception)
try:
raise TypeError("Again !?!")
except:
pass
# end of useful stuff
finally:
# Display the *original* exception
traceback.print_exception(*exc_info)
del exc_info
Producing:
Traceback (most recent call last):
File "t.py", line 6, in <module>
raise TypeError("Oups!")
TypeError: Oups!
Few pitfalls with this though:
From the doc of
sys_info:Assigning the traceback return value to a local variable in a function that is handling an exception will cause a circular reference. This will prevent anything referenced by a local variable in the same function or by the traceback from being garbage collected. [...] If you do need the traceback, make sure to delete it after use (best done with a try ... finally statement)
but, from the same doc:
Beginning with Python 2.2, such cycles are automatically reclaimed when garbage collection is enabled and they become unreachable, but it remains more efficient to avoid creating cycles.
On the other hand, by allowing you to access the traceback associated with an exception, Python 3 produce a less surprising result:
import traceback
try:
raise TypeError("Oups!")
except Exception as err:
try:
raise TypeError("Again !?!")
except:
pass
traceback.print_tb(err.__traceback__)
... will display:
File "e3.py", line 4, in <module>
raise TypeError("Oups!")
The answer to this question depends on the version of Python you're using.
In Python 3
It's simple: exceptions come equipped with a __traceback__ attribute that contains the traceback. This attribute is also writable, and can be conveniently set using the with_traceback method of exceptions:
raise Exception("foo occurred").with_traceback(tracebackobj)
These features are minimally described as part of the raise documentation.
All credit for this part of the answer should go to Vyctor, who first posted this information. I'm including it here only because this answer is stuck at the top, and Python 3 is becoming more common.
In Python 2
It's annoyingly complex. The trouble with tracebacks is that they have references to stack frames, and stack frames have references to the tracebacks that have references to stack frames that have references to... you get the idea. This causes problems for the garbage collector. (Thanks to ecatmur for first pointing this out.)
The nice way of solving this would be to surgically break the cycle after leaving the except clause, which is what Python 3 does. The Python 2 solution is much uglier: you are provided with an ad-hoc function,sys.exc_info(), which only works inside the except clause. It returns a tuple containing the exception, the exception type, and the traceback for whatever exception is currently being handled.
So if you are inside the except clause, you can use the output of sys.exc_info() along with the traceback module to do various useful things:
>>> import sys, traceback
>>> def raise_exception():
... try:
... raise Exception
... except Exception:
... ex_type, ex, tb = sys.exc_info()
... traceback.print_tb(tb)
... finally:
... del tb
...
>>> raise_exception()
File "<stdin>", line 3, in raise_exception
But as your edit indicates, you're trying to get the traceback that would have been printed if your exception had not been handled, after it has already been handled. That's a much harder question. Unfortunately, sys.exc_info returns (None, None, None) when no exception is being handled. Other related sys attributes don't help either. sys.exc_traceback is deprecated and undefined when no exception is being handled; sys.last_traceback seems perfect, but it appears only to be defined during interactive sessions.
If you can control how the exception is raised, you might be able to use inspect and a custom exception to store some of the information. But I'm not entirely sure how that would work.
To tell the truth, catching and returning an exception is kind of an unusual thing to do. This might be a sign that you need to refactor anyway.
Since Python 3.0[PEP 3109] the built in class Exception has a __traceback__ attribute which contains a traceback object (with Python 3.2.3):
>>> try:
... raise Exception()
... except Exception as e:
... tb = e.__traceback__
...
>>> tb
<traceback object at 0x00000000022A9208>
The problem is that after Googling __traceback__ for a while I found only few articles but none of them describes whether or why you should (not) use __traceback__.
However, the Python 3 documentation for raise says that:
A traceback object is normally created automatically when an exception is raised and attached to it as the
__traceback__attribute, which is writable.
So I assume it's meant to be used.