Why exc_traceback returns None

Question

sys.exc_info() returns a tuple (type , value, traceback).
so sys.exc_info()[2] is our traceback object.

Why it does not catch exceptions traceback with this code:

import sys

try:
    1/0
except ZeroDivisionError:
    print sys.exc_info()[2].tb_frame.f_back

tb_frame and f_back usage has been explained here: Frame Objects

Answer 1

You see None because there is no outer frame. You're executing this directly, so the current frame is the last frame. To demonstrate this, I created a demo.py:

import sys

try:
    1/0
except ZeroDivisionError:
    print sys.exc_info()[2].tb_frame.f_back

which should look familiar, and a trivial caller.py:

import demo

Now see the difference:

$ python demo.py
None

$ python caller.py
<frame object at 0x10bc34c20>

In the second case, where there is an outer frame (i.e. caller.py), you don't see None.