It wouldn't be difficult to have a list of trace functions, so that
every line of "real" Python executed, would invoke all the trace
functions. But Ram has asked for something more: when the first trace
function is executing, its line should themselves be traced by the
remaining trace functions in the list. Presumably the lines in the
second trace function should also be traced by the function third in the
list, and so on. This is the thing that will be difficult to accomplish.
--Ned.
On 4/25/19 2:02 PM, Anders Hovmöller wrote:
Well, it would trigger the top level chaining trace function, but they
should be able to decide when to call the sub-trace functions. Hmm...
Maybe :)
On 25 Apr 2019, at 19:16, Ned Batchelder <n...@nedbatchelder.com
<mailto:n...@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 <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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