gh-142654: show the clear error message when sampling on an unknown PID

[kemingy]

Before this change:

OSError: Cannot open process memory map file '/proc/-1/maps' for PID -1 section search: No such file or directory
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/keming/GitHub/cpython/Lib/runpy.py", line 196, in _run_module_as_main
return _run_code(code, main_globals, None,
"__main__", mod_spec)
File "/home/keming/GitHub/cpython/Lib/runpy.py", line 87, in _run_code
exec(code, run_globals)
~~~~^^^^^^^^^^^^^^^^^^^
File "/home/keming/GitHub/cpython/Lib/profiling/sampling/__main__.py", line 64, in <module>
main()
~~~~^^
File "/home/keming/GitHub/cpython/Lib/profiling/sampling/cli.py", line 592, in main
handler(args)
~~~~~~~^^^^^^
File "/home/keming/GitHub/cpython/Lib/profiling/sampling/cli.py", line 620, in _handle_attach
collector = sample(
args.pid,
...<8 lines>...
opcodes=args.opcodes,
)
File "/home/keming/GitHub/cpython/Lib/profiling/sampling/sample.py", line 327, in sample
profiler = SampleProfiler(
pid,
...<7 lines>...
collect_stats=realtime_stats,
)
File "/home/keming/GitHub/cpython/Lib/profiling/sampling/sample.py", line 39, in __init__
self.unwinder = _remote_debugging.RemoteUnwinder(
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
self.pid, all_threads=self.all_threads, mode=mode, native=native, gc=gc,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
opcodes=opcodes, skip_non_matching_threads=skip_non_matching_threads,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cache_frames=True, stats=collect_stats
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
RuntimeError: Failed to find the PyRuntime section in process -1 on Linux platform

After this change:

Failed to find the PyRuntime section in process -1 on Linux platform

This aligns the behavior with attaching to a process that doesn't have the PyRuntime section.

• Issue: Unfriendly traceback when sampling from an unknown PID #142654

[Copilot]

Pull request overview

This PR improves error handling when attempting to profile a process with an invalid PID by simplifying the error message. Instead of showing a confusing stack trace with multiple exceptions, it now displays only the final, clear error message about failing to find the PyRuntime section.

Key Changes:

• Wraps RemoteUnwinder initialization in a try-except block that converts exceptions to SystemExit
• Updates test expectations from OSError/RuntimeError to SystemExit
• Adds a NEWS entry documenting the improvement

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
Lib/profiling/sampling/sample.py	Adds exception handling in SampleProfiler.__init__ to convert errors to SystemExit for cleaner user-facing messages
Lib/test/test_profiling/test_sampling_profiler/test_integration.py	Updates test to expect SystemExit instead of OSError/RuntimeError for invalid PIDs
Misc/NEWS.d/next/Library/2025-12-13-10-34-59.gh-issue-142654.fmm974.rst	Documents the error message improvement

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[pablogsal]

@kemingy can you approach this similarly as #142592 ? The idea is to not show an ugly stack trace or difficult to understand messages like "Failed to find the PyRuntime section in process -1 on Linux platform" but just checking if the process exists or not or if is valid or not

[kemingy]

@kemingy can you approach this similarly as #142592 ? The idea is to not show an ugly stack trace or difficult to understand messages like "Failed to find the PyRuntime section in process -1 on Linux platform" but just checking if the process exists or not or if is valid or not

Hi @pablogsal I have added the process check. Please take a look.

[pablogsal]

I would prefer to raise some custom exception here and catch it in __main__ like the other exceptions. Perhaps we should also do the same for the other usages of sys.exit.

Do you mind creating a errors.py file with custom exceptions for the different case, raise them and properly handle the messages in __main__?

[pablogsal]

We also need a test for this

[kemingy]

We also need a test for this

Hi @pablogsal Thanks for your advice. I have added the errors.py file and handle these custom exceptions in the __main__. Also added a test for the attach cli. Please take a look.

[pablogsal]

Made some small fixes but great job @kemingy! Thanks for the PR 🚀