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Bug description:
I'm using coverage and pytest-cov in CI to measure the line coverage of the unittests. It is achieved by registering a trace function with sys.settrace.
However, after binsecting my unittests, I found that when a RecursionError is raised, the system trace function will be cleared. That will cause a warning emitted by coverage:
~/Projects/cpython/venv/lib/python3.15t/site-packages/coverage/pytracer.py:355: CoverageWarning: Trace function changed, data is likely wrong: None != <bound method PyTracer._trace of <PyTracer at 0x200021dcc20: 2076 data points in 11 files>> (trace-changed)
self.warn(Reproducible code:
import sys
def tracer(*args, **kwargs):
pass
def factorial(n: int) -> int:
"""Calculate the factorial of a number."""
if n <= 1:
return 1
return n * factorial(n - 1)
sys.settrace(tracer)
assert sys.gettrace() is tracer
sys.setrecursionlimit(64)
assert sys.gettrace() is tracer
try:
_ = factorial(100)
except RecursionError:
pass
assert sys.gettrace() is NoneREPL Output:
# Add a code block here, if required
$ python3
Python 3.13.3 (main, Apr 8 2025, 13:54:08) [Clang 16.0.0 (clang-1600.0.26.6)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> def tracer(*args, **kwargs):
... pass
...
>>> def factorial(n):
... if n <= 1:
... return 1
... return n * factorial(n - 1)
...
>>> sys.settrace(tracer)
>>> sys.gettrace() is tracer
True
>>> sys.setrecursionlimit(64)
>>> _ = factorial(100)
Traceback (most recent call last):
File "<python-input-6>", line 1, in <module>
_ = factorial(100)
File "<python-input-2>", line 4, in factorial
return n * factorial(n - 1)
~~~~~~~~^^^^^^^
File "<python-input-2>", line 4, in factorial
return n * factorial(n - 1)
~~~~~~~~^^^^^^^
File "<python-input-2>", line 4, in factorial
return n * factorial(n - 1)
~~~~~~~~^^^^^^^
[Previous line repeated 51 more times]
File "<python-input-2>", line 1, in factorial
def factorial(n):
RecursionError: maximum recursion depth exceeded
>>> sys.gettrace() is None
TrueCPython versions tested on:
CPython main branch
Operating systems tested on:
macOS
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