sys.monitoring fails to run callback on small function calls

[sczi]

Bug report

Bug description:

With a basic use of sys.monitoring to report calls of a function, everything works as expected:

from sys import monitoring


def foo():
    for i in range(5):
        if i > 4:
            return "in foo"


monitoring.use_tool_id(0, "test")


def tracer(code, instruction_offset, c, arg0):
    print("got args: ", arg0)


monitoring.register_callback(0, monitoring.events.CALL, tracer)
monitoring.set_local_events(0, foo.__code__, monitoring.events.CALL)

print(foo())

but if we modify foo to just be:

def foo():
    return "in foo"

now tracer doesn't run. python supposedly doesn't do any inlining, but it seems that on simple trivially inlineable functions, that the CALL event isn't being triggered?

I tested this on python3.13.3 and against the latest git (Python 3.15.0a0 (heads/main:aec7f5f8b2e))

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

[sczi]

Sorry I think I misunderstood the set_local_events api. It doesn't work for tracing calls to a specific function anywhere in your codebase, but for enabling tracing within that code object. For example:

from sys import monitoring


def foo(x, y):
    print("hello")
    for i in range(5):
        if i > 3:
            return x + y


monitoring.use_tool_id(0, "test")


def tracer(code, instruction_offset, callable, args):
    print("tracing callable:", callable)
    print("got args:", args)


monitoring.register_callback(0, monitoring.events.CALL, tracer)
monitoring.set_local_events(0, foo.__code__, monitoring.events.CALL)

print(foo(3, 5))

prints:

tracing callable: <built-in function print>
got args: hello
hello
tracing callable: <class 'range'>
got args: 5
8