How to stay inside the debugger after encountering an error?

Question

When I debug a loop, the debugger quits when it encounters an error. Is it possible to stay inside the debugger so that I can investigate the program's state right before the error?

For example,

import pdb;pdb.set_trace()

for i in [1, 2, 3, 0]:
    print(2/i)

I would like to hit c so that the debugger keeps running through the loop until the last iteration. Then, instead of quitting, the debugger stays active so that I can look at what is the value of i that is causing the error.

`python -m pdb -c continue myscript.py` : https://stackoverflow.com/questions/242485/starting-python-debugger-automatically-on-error would help — ymonad, Jan 25 '19 at 04:11

score 0 · Answer 1 · answered Jan 25 '19 at 04:01

What you are looking for is pdb.post_mortem. The code that may fail should be encapsulated in a try/except block, with the handler invoking that function, for example:

try:
    for i in [1, 2, 3, 0]:
        print(2/i)
except Exception:
    import pdb
    pdb.post_mortem()

Execution:

2.0
1.0
0.6666666666666666
> (3)<module>()
-> print(2/i)
(Pdb)

The pdb shell is now at the point of failure.

How to stay inside the debugger after encountering an error?

1 Answers1