`--pdb` support to debug error on task execution

Support post-mortem debugger for unhadled task execution exceptions.

This must handled separately from exceptions on load time. Because doit catches tasks errors and keep running…

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(original report)

I’m trying to debug a doit pipeline and need to break into pdb in a library I’m using from doit. Unfortunately, doit captures all in- and output, which I have to undo everywhere I’m trying to debug. Would be nice to have the above mentioned parameter that lets me just do import pdb; pdb.set_trace() (or breakpoint() in the upcoming Python 3.7).

For reference, this is the code I currently use to break into pdb:

try:
    code_that_crashes_somewhere_in_your_pipeline
except KeyError:
    import pdb, sys; 
    d = pdb.Pdb(stdin=sys.__stdin__, stdout=sys.__stdout__)
    d.reset(); t = sys.exc_info()[2]; d.interaction(None, t)

[schettino72]

pytest has the --pdb switch which will launch a pdb shell at the point of the exception

Like this: http://pydoit.org/cmd_run.html#pdb 😁

But this only works to debug issues that happen when loading tasks. Not on task execution… actually I too wished sometimes it would work to debug actual task execution.

[madig]

I googled “python doit debug” but must embarrassingly admit that I scrolled over your link. Oops.

The snippet I use above has the nice property to break into pdb where the exception occurs without me having to know in advance where exactly it occurs. pytest has the --pdb switch which will launch a pdb shell at the point of the exception (https://docs.pytest.org/en/latest/usage.html#dropping-to-pdb-python-debugger-on-failures). I think that would be useful to have in doit, too.