[Python-ideas] Verbose traceback formatting

[Calvin Spealman]

On Tue, Aug 28, 2012 at 6:26 PM, Mike Graham <mikegraham at gmail.com> wrote:
> It's possible to give a lot more on error than the default traceback
> gives you. I propose that Python should ship a more verbose formatter
> and a command line switch to use it.
>
> Here's an example of IPython's verbose formatter. I wrote a buggy program:
>
>> def f(a):
>>     x = a * 4
>>     y = a - 4
>>     return x / y
>>
>> def main():
>>     for i in xrange(100):
>>         f(i)
>>
>> main()
>
>
> and then ran it in IPython with verbose tracebacks and got the following output:
>
>> ZeroDivisionError                         Traceback (most recent call last)
>>
>> /home/mike/foo.py in <module>()
>>       8         f(i)
>>       9
>> ---> 10 main()
>>         global main = <function main at 0x10bd7d0>
>>      11
>>      12
>>
>> /home/mike/foo.py in main()
>>       6 def main():
>>       7     for i in xrange(100):
>> ----> 8         f(i)
>>         global f = <function f at 0x10bd758>
>>         i = 4
>>       9
>>      10 main()
>>
>> /home/mike/foo.py in f(a=4)
>>       2     x = a * 4
>>       3     y = a - 4
>> ----> 4     return x / y
>>         x = 16
>>         y = 0
>>       5
>>       6 def main():
>>
>> ZeroDivisionError: integer division or modulo by zero
>
>
>
> This is very handy! The reprs of all locals are input so I can see
> what the values of a, x, and y were when I had my error and there are
> a few lines of code on either side of the line that matters to help me
> get oriented. The former feature is the more powerful one, although
> enabling this by default is a bad idea; (first and foremost, this can
> be a security hazard). I can't count how many trips into pdb this
> would have saved me.
>
> I think having this feature be part of Python itself would be very
> helpful to new learners and to those helping them. I constantly deal
> with learners seeking help who are unable to clearly provide the
> actual values and types of the objects in the code they're having
> trouble with; it would be nice simply to say, "Show me a verbose
> traceback" and might even help them to debug their code without
> assistance.

+1 on the more verbose formatter in stdlib

Rather than a glad, I'd like to see the path to a formatter, so you
can use more than just the two builtin. It would be great to easily
define my own and have that used in all cases.

python -t traceback.VerboseFormatter my_broken_script.py

> Mike
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