Get full traceback

Question

How can i get full traceback in the following case, including the calls of func2 and func functions?

import traceback

def func():
         


        

Answer 1

As mechmind answered, the stack trace consists only of frames between the site where the exception was raised and the site of the try block. If you need the full stack trace, apparently you're out of luck.

Except that it's obviously possible to extract the stack entries from top-level to the current frame—traceback.extract_stack manages it just fine. The problem is that the information obtained by traceback.extract_stack comes from direct inspection of stack frames without creating a traceback object at any point, and the logging API requires a traceback object to affect traceback output.

Fortunately, logging doesn't require an actual traceback object, it requires an object that it can pass to the formatting routines of the traceback module. traceback doesn't care either—it only uses two attributes of the traceback, the frame and the line number. So, it should be possible to create a linked list of duck-typed faux-traceback objects and pass it off as the traceback.

import sys

class FauxTb(object):
    def __init__(self, tb_frame, tb_lineno, tb_next):
        self.tb_frame = tb_frame
        self.tb_lineno = tb_lineno
        self.tb_next = tb_next

def current_stack(skip=0):
    try: 1/0
    except ZeroDivisionError:
        f = sys.exc_info()[2].tb_frame
    for i in xrange(skip + 2):
        f = f.f_back
    lst = []
    while f is not None:
        lst.append((f, f.f_lineno))
        f = f.f_back
    return lst

def extend_traceback(tb, stack):
    """Extend traceback with stack info."""
    head = tb
    for tb_frame, tb_lineno in stack:
        head = FauxTb(tb_frame, tb_lineno, head)
    return head

def full_exc_info():
    """Like sys.exc_info, but includes the full traceback."""
    t, v, tb = sys.exc_info()
    full_tb = extend_traceback(tb, current_stack(1))
    return t, v, full_tb

With these functions in place, your code only requires a trivial modification:

import logging

def func():
    try:
        raise Exception('Dummy')
    except:
        logging.error("Something awful happened!", exc_info=full_exc_info())

def func2():
    func()

func2()

...to give the expected output:

ERROR:root:Something awful happened!
Traceback (most recent call last):
  File "a.py", line 52, in 
    func2()
  File "a.py", line 49, in func2
    func()
  File "a.py", line 43, in func
    raise Exception('Dummy')
Exception: Dummy

Note that the faux-traceback objects are fully usable for introspection—displaying local variables or as argument to pdb.post_mortem()—because they contain references to real stack frames.