Custom python traceback or debug output

Question

I have a traceback print and want to customize the last part of it.

What: The error occurred in another process and traceback lies there (as is the case in multiprocessing).
Problem: I want to have the full traceback and error report.

Similar to this code:

>>> def f():
    g()

>>> def g():
    raise Exception, Exception(), None ## my traceback here

>>> f()

Traceback (most recent call last):
  File "<pyshell#14>", line 1, in <module>
    f()
  File "<pyshell#8>", line 2, in f
    g()
  File "<pyshell#11>", line 2, in g
    raise Exception, Exception(), None ## my traceback starts here
my traceback appears here
my traceback appears here

Exception

Impossible "Solutions": subclass and mock-object

>>> from types import *
>>> class CostomTB(TracebackType):
    pass


Traceback (most recent call last):
  File "<pyshell#125>", line 1, in <module>
    class CostomTB(TracebackType):
TypeError: Error when calling the metaclass bases
    type 'traceback' is not an acceptable base type
>>> class CostomTB(object):
    pass

>>> try: zzzzzzzzz
except NameError:
    import sys
    ty, err, tb = sys.exc_info()
    raise ty, err, CostomTB()


Traceback (most recent call last):
  File "<pyshell#133>", line 5, in <module>
    raise ty, err, CostomTB()
TypeError: raise: arg 3 must be a traceback or None

I am using python 2.7.

NIlesh Sharma · Accepted Answer · 2012-08-09 21:51:05Z

1

I guess you want the full traceback stack. See this which is having very good examples python logging module.
If some confusion comes See the logging documentation.

answered Aug 9, 2012 at 21:51

NIlesh Sharma

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Comments

Stefano Masini · Accepted Answer · 2012-08-10 08:26:40Z

You mentioned a separate process: if your problem is to capture the traceback in process A and show it in process B, as if the exception was actually raised in the latter, then I'm afraid there is no clean way to do it.

I would suggest to serialize the traceback in process A, send it to process B and from there raise a new exception that includes the former in its description. The result is a somewhat longer output, but it carries information about both processes stacks.

In the following example there aren't really two separate processes, but I hope it makes my point clearer:

import traceback, StringI

def functionInProcessA():
    raise Exception('Something happened in A')

class RemoteException(Exception):
    def __init__(self, tb):
        Exception.__init__(self, "Remote traceback:\n\n%s" % tb)

def controlProcessB():
    try:
        functionInProcessA()
    except:
        fd = StringIO.StringIO()
        traceback.print_exc(file=fd)
        tb = fd.getvalue()
        raise RemoteException(tb)

if __name__ == '__main__':
    controlProcessB()

Output:

Traceback (most recent call last):
  File "a.py", line 20, in <module>
    controlProcessB()
  File "a.py", line 17, in controlProcessB
    raise RemoteException(tb)
__main__.RemoteException: Remote traceback:

Traceback (most recent call last):
  File "a.py", line 12, in controlProcessB
    functionInProcessA()
  File "a.py", line 4, in functionInProcessA
    raise Exception('Something happened in A')
Exception: Something happened in A

I implemented your idea: github.com/amintos/akira/blob/playground/process/…

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