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

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[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