tempfile.TemporaryFile() emits a ResourceWarning that does not trace back to user code

[mmerickel]

Feature or enhancement

When using tempfile.TemporaryFile a ResourceWarning should be emitted with the source tracing back to user code. Instead it currently traces back to the _io.open invocation inside the tempfile module and is useless for tracking down the code that created the tempfile.

Pitch

Take the following foo.py:

import tempfile


def main():
    fp = tempfile.TemporaryFile()


if __name__ == '__main__':
    main()

I would expect the ResourceWarning to point to the line fp = tempfile.TemporaryFile(). Instead I see the following:

❯ PYTHONTRACEMALLOC=1 PYTHONWARNINGS=default python3 -m foo
/Users/michael/work/foo.py:9: ResourceWarning: unclosed file <_io.BufferedRandom name=3>
  main()
Object allocated at (most recent call last):
  File "/opt/homebrew/Cellar/python@3.11/3.11.2_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/tempfile.py", lineno 657
    file = _io.open(dir, mode, buffering=buffering,

Note that it's pointing at the tempfile module itself which is worthless other than to tell me it's a tempfile that's causing the issue - however for me it's in library code and I have no idea which library!

Please modify tempfile to properly track the source and emit a better warning.

[tomasr8]

The documentation says that you can pass a number to PYTHONTRACEMALLOC which is the maximum number of frames it stores. Using PYTHONTRACEMALLOC=1 stores just 1 frame.

With PYTHONTRACEMALLOC=3 (or higher), you should see the full trace:

foo.py:9: ResourceWarning: unclosed file <_io.BufferedRandom name=3>
  main()
Object allocated at (most recent call last):
  File "foo.py", lineno 9
    main()
  File "foo.py", lineno 5
    fp = tempfile.TemporaryFile()
  File "/home/tomas/.pyenv/versions/3.11.2/lib/python3.11/tempfile.py", lineno 622
    file = _io.open(dir, mode, buffering=buffering,

[mmerickel]

Confirmed this is working for me to track down those leaks - I had no idea that this was possible with the tracemalloc config. I'm going to close this issue. Thank you @tomasr8!