Fix possible dataloss during finalization with GzipFile #159422

Bug report

After stumbling into #159419, which addresses possible dataloss during finalization. I decided to take a quick pass across some of our other writers to see if the same bug exists elsewhere. I came across this issue in GzipFile, where trying to import a module at finalization could trigger an ImportError that results in the file never being properly closed.

current implementation

def __del__(self):
    if self.mode == WRITE and not self.closed:
        import warnings  # If warnings fails to load
        warnings.warn("unclosed GzipFile",
                      ResourceWarning, source=self, stacklevel=2)

    super().__del__()  # then, this line will never run

example

import gzip
f = gzip.open("out.gz", "wb")
f.write(b"important data\n" * 1000)
# never explicitly closed; finalized at shutdown

$ python repro.py
Exception ignored while calling deallocator <function GzipFile.__del__ ...>:
ImportError: sys.meta_path is None, Python is likely shutting down

CPython versions tested on:

3.14, 3.15, 3.16

Operating systems tested on:

No response

Linked PRs

• gh-159422: Always close GzipFile in __del__ even if the warning fails #159423