NamedTemporaryFile doesn't issue a ResourceWarning when left unclosed on POSIX

Bug report

Bug description:

import sys
import tempfile


def main():
    tempfile.NamedTemporaryFile()

if __name__ == "__main__":
    sys.exit(main())

when run with python -Werror demo.py nothing happens

if you open a file normally you get a ResourceWarning:

import sys
import tempfile


def main():
    open("example", "w")

if __name__ == "__main__":
    sys.exit(main())

 graingert@conscientious  ~/projects/temp_file_resource_warnings  python -Werror demo2.py
Exception ignored in: <_io.FileIO name='example' mode='wb' closefd=True>
Traceback (most recent call last):
  File "/home/graingert/projects/temp_file_resource_warnings/demo2.py", line 6, in main
    open("example", "w")
ResourceWarning: unclosed file <_io.TextIOWrapper name='example' mode='w' encoding='UTF-8'>

it appears that you do get a ResourceWarning on windows, but I've only seen it in CI I havn't reproduced locally yet

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Linked PRs

gh-126639: Add ResourceWarning to NamedTemporaryFile #126677

I think this __del__ needs to issue the resource warning:

cpython/Lib/tempfile.py

Lines 471 to 472 in 450db61

    
           def __del__(self): 
        
               self.cleanup()

I don't see how that's related? The resource delete on __del__ is a last resort, and it needs to issue a ResourceWarning so that code that fails to finalise explicitly can be detected

Ah sorry, I misunderstood the "open again" in the sense that you can leave the descriptor hanging. My bad. However, non-named temporary files say:

It will be destroyed as soon as it is closed (including an implicit close when the object is garbage collected).

Should implicit close emit a warning in this case? Actually, why is there a warning on Windows?

Should implicit close emit a warning in this case?

Yes, all implicit closing of resources on GC should issue a ResourceWarning

I suspect the way to go here is to replace _TemporaryFileCloser with a weakref.finalize

I suspect the way to go here is to replace _TemporaryFileCloser with a weakref.finalize

Looks like it, TemporaryDirectory is doing something similar:

cpython/Lib/tempfile.py

Lines 885 to 888 in 450db61

    
           self._finalizer = _weakref.finalize( 
        
               self, self._cleanup, self.name, 
        
               warn_message="Implicitly cleaning up {!r}".format(self), 
        
               ignore_errors=self._ignore_cleanup_errors, delete=self._delete)

pythongh-126639: Add ResourceWarning to NamedTemporaryFile

gh-126639: Add ResourceWarning to NamedTemporaryFile (#126677)

Categorizing it as a feature as per #126677 (comment).

pythongh-126639: Add ResourceWarning to NamedTemporaryFile (python#12…

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NamedTemporaryFile doesn't issue a ResourceWarning when left unclosed on POSIX #126639

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

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	self._finalizer = _weakref.finalize(
	self, self._cleanup, self.name,
	warn_message="Implicitly cleaning up {!r}".format(self),
	ignore_errors=self._ignore_cleanup_errors, delete=self._delete)

NamedTemporaryFile doesn't issue a ResourceWarning when left unclosed on POSIX #126639

Description

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

Activity

graingert commented on Nov 10, 2024

picnixz commented on Nov 10, 2024

graingert commented on Nov 10, 2024

picnixz commented on Nov 10, 2024

graingert commented on Nov 10, 2024

graingert commented on Nov 10, 2024

tomasr8 commented on Nov 10, 2024

picnixz commented on Dec 19, 2024

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