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profiling.sampling is not working for replay mode #148225

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profiling.sampling is not working for replay mode#148225
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stdlibStandard Library Python modules in the Lib/ directorytopic-profilingtype-bugAn unexpected behavior, bug, or error

Description

@seanleeee13
seanleeee13
opened on Apr 7, 2026

Bug report

Bug description:

I ran next command with a.py code, and it made the error.

python3.15 -m profiling.sampling run -o output.prof a.py
python3.15 -m profiling.sampling replay output.prof

# a.py
for i in range(10000):
    a = [*p for p in [[1, 2], [2], [3, 4, 4]]]

This is the error message:

Traceback (most recent call last):
  File "<frozen runpy>", line 196, in _run_module_as_main
  File "<frozen runpy>", line 87, in _run_code
  File "C:\Users\XXX\AppData\Local\Python\pythoncore-3.15-64\Lib\profiling\sampling\__main__.py", line 65, in <module>
    main()
    ~~~~^^
  File "C:\Users\XXX\AppData\Local\Python\pythoncore-3.15-64\Lib\profiling\sampling\cli.py", line 788, in main
    _main()
    ~~~~~^^
  File "C:\Users\XXX\AppData\Local\Python\pythoncore-3.15-64\Lib\profiling\sampling\cli.py", line 922, in _main
    handler(args)
    ~~~~~~~^^^^^^
  File "C:\Users\XXX\AppData\Local\Python\pythoncore-3.15-64\Lib\profiling\sampling\cli.py", line 1175, in _handle_replay
    with BinaryReader(args.input_file) as reader:
         ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "C:\Users\XXX\AppData\Local\Python\pythoncore-3.15-64\Lib\profiling\sampling\binary_reader.py", line 32, in __enter__
    self._reader = _remote_debugging.BinaryReader(self.filename)
                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
ValueError: Invalid magic number: 0xfa03a97b

The reported magic number 0xfa03a97b corresponds to Python 3.13/3.14. It seems that profiling.sampling might be inadvertently picking up components or generating data using the 3.14 environment available on the PATH, even when explicitly invoked with python3.15.
I used python 3.15.0a7, and I also downloaded python 3.14.3, and only 3.14.3 is on PATH.
Environments - Window 11 64bit, Using VSCode powershell terminal, pwsh 7.5.5
Also, I tried to do this in venv but python -m profiling.sampling run -o output.prof a.py made another error.
Failed to find the PyRuntime section in process 15236 on Windows platform

CPython versions tested on:

3.15

Operating systems tested on:

Windows

Linked PRs

Activity

  1. seanleeee13
    added
    type-bugAn unexpected behavior, bug, or error
    on Apr 7, 2026
  2. StanFromIreland
    added
    stdlibStandard Library Python modules in the Lib/ directory
    topic-profiling
    on Apr 7, 2026

  3. Ignyra commented on Apr 7, 2026

    @Ignyra
    Ignyra
    on Apr 7, 2026

    I looked into this a bit, and it seems that the initial error comes from reading the data as the binary format while the original command produced a default pstats output. The replay command only works with binary format files that can be generated using --binary, and it doesn’t validate the input format, so passing a pstats file leads to the confusing error in which the BinaryReader expected a magic number in the header where it is only generated for binary files. I think this should work as expected:

    python -m profiling.sampling run --binary -o output.prof test.py
python -m profiling.sampling replay output.prof

  4. seanleeee13 commented on Apr 7, 2026

    @seanleeee13
    seanleeee13
    on Apr 7, 2026
    Author

    I tried to do with --binary option, and it made Failed to find the PyRuntime section in process 26260 on Windows platform error, a simmilar error with when using venv.

  5. seanleeee13 commented on Apr 7, 2026

    @seanleeee13
    seanleeee13
    on Apr 7, 2026
    Author

    Tried with another a.py - and it worked.

    import time

for i in range(1000000):
    a = [p for p in [[1, 2], [2], [3, 4, 4]]]
    if i % 100000 == 0:
        time.sleep(0.1)

    I think it could be an error because a.py is to short for sampling.
    Also, I updated to python 3.15.0a8, but it doesn't work on venv yet.

  6. Ignyra commented on Apr 8, 2026

    @Ignyra
    Ignyra
    on Apr 8, 2026

    I tried to reproduce this on Windows with Python 3.15.0a8, but I wasn’t able to hit the same error. It might be related to something environment-specific.

  7. pablogsal
    added 3 commits that reference this issue on Apr 8, 2026

    pythongh-148225: Validate profiling.sampling replay input

    6103ec8

    pythongh-148225: Validate profiling.sampling replay input

    7491220

    pythongh-148225: Validate profiling.sampling replay input

    0ddd95c

  8. pablogsal commented on Apr 8, 2026

    @pablogsal
    pablogsal
    on Apr 8, 2026
    Member

    Yeah I think the only bug here that we can validate is that the binary files are not validated before checking and the error is confusing. I will work on a fix

  9. pablogsal
    added 2 commits that reference this issue on Apr 8, 2026

    pythongh-148225: Validate profiling.sampling replay input

    48bd6dd

    gh-148225: Validate profiling.sampling replay input (#148243)

    efde433
  10. pablogsal
    closed this as completedon Apr 9, 2026

  11. pablogsal commented on Apr 9, 2026

    @pablogsal
    pablogsal
    on Apr 9, 2026
    Member

    Thanks for the report!

  12. ljfp
    added a commit that references this issue on Apr 25, 2026

    pythongh-148225: Validate profiling.sampling replay input (python#148243

    fb321a7
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