To clarify, I meant that each trace function would manually call any trace functions that were registered below it, instead of using the trampoline in cpython. Does that solve the problem you raised? On Thu, Apr 25, 2019, 20:20 Ned Batchelder <ned@nedbatchelder.com> wrote:
Perhaps I misunderstand what's implied by "simple(!) monkeypatch of sys.settrace", but the trickiest part of Ram's proposal is that the body of one trace function would still trigger the remaining trace functions. That to me sounds like it's going to require changes to ceval.c
--Ned. On 4/25/19 12:26 PM, Ram Rachum wrote:
Hmm, looks like, for this to work, you'll need the existing tracer to be cooperative. Right now there are existing tracers, for example coverage's tracer and Wing IDE's tracer, and I would need to modify them for your idea to work, right?
If I understand your idea correctly, the first tracer would monkeypatch `sys.settrace` so whenever someone else adds a tracer, it doesn't really do `sys.settrace` but just add a function that the real tracer would be calling after it's done tracing. But this can't really be done without the original tracer implementing it, right?
On Thu, Apr 25, 2019 at 6:16 PM Ram Rachum <ram@rachum.com> wrote:
Oh wow, I didn't even consider that. I think you're right, I'll do more thinking about this. Thanks Anders!
On Thu, Apr 25, 2019 at 6:10 PM Anders Hovmöller <boxed@killingar.net> wrote:
Can't this be implemented today by a simple monkey patch of sys.settrace?
On 25 Apr 2019, at 16:51, Ram Rachum <ram@rachum.com> wrote:
Hi,
Here's something I want in Python: Multiple levels of tracers working on top of each other, instead of just one.
I'm talking about the tracer that one can set by calling sys.settrace.
I've recently released PySnooper: https://github.com/cool-RR/PySnooper/
One of the difficulties I have, is that I can't debug or run the `coverage` tool on the core of this module. That's because the core is a trace function, and debuggers and coverage tools work by setting a trace function. When PySnooper sets its trace function using `sys.settrace`, the code that runs in that trace function runs without getting traced by the coverage tracer.
This means that people who develop debuggers and coverage tools can't use a debugger or a coverage tool on the core of their tool. It's quite an annoying problem.
My proposed solution: Multiple levels of tracing, instead of just one. When you install a tracer, you're not replacing the existing one, you're appending a tracer to the existing list of tracers.
If this was implemented, then when PySnooper would install its tracer, the coverage tracer would still be active and running, for every line of code including the ones in PySnooper's tracer.
Obviously, we'll need to figure out the API and any other kind of problems with this proposal.
What do you think?
Thanks, Ram.
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