[Python-Dev] API design question: how to extend sys.settrace()? (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Wed Sep 27 20:28:52 EDT 2017

On 28 September 2017 at 06:23, George King <gwk.lists at gmail.com> wrote:

Victor, thank you for starting this conversation. Nick, I just looked at your patch and I think it is a better solution than mine, because it does not involve adding to or changing the sys API. I will close my pull request.

The reason for my interest in this area is that I’m experimenting with a code coverage tool that does per-opcode tracing. I just updated it to use the new ftraceopcodes feature and it almost worked: Nick’s implementation calls the opcode trace before updating the line number, whereas my version updated line numbers first, so the event stream is slightly different. See: https://github.com/python/cpython/commit/5a8516701f5140c8c989c40e261a4f4e20e8af86#diff-7f17c8d8448b7b6f90549035d2147a9f From my perspective it makes more sense to do the update to flineno first, followed by the opcode trace, because then line events and opcode events corresponding to the same opcode will have the same line number; as it is they come out different. Is the current order intentional? Otherwise I’ll submit a patch.

Line numbers simply weren't relevant to my use case (injecting inconveniently timed exceptions), so I never checked whether or not f_lineno was accurate when the trace event was emitted.

So yeah, a follow-up bug report and PR to fix that would be appreciated (no need for a NEWS entry, since it's a bug in a not-yet-released feature).

Cheers, Nick.

-- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia

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