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 <r...@rachum.com
<mailto:r...@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
<bo...@killingar.net <mailto:bo...@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 <r...@rachum.com
<mailto:r...@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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