Feature or enhancement

Proposal:

This may indicate accidental data loss.

Ways to make sure all data is written:

1. Use the file-like object as a “With Statement Context Manager”.
   • All objects which inherit from IOBase support this.
   • BufferedIOBase, BufferedWriter, and GzipFile all support this.
   • Ensures .close() is called in both exception and regular cases.
2. Ensure .close() is always called which flushes data before closing.
3. If the underlying stream need to be kept open, use .detach()

Since 3.12 flushing has been necessary in GzipFile (see gh-105808 which was a release blocker), this makes that more visible. Users have been encountering as they upgrade to 3.12 (ex. gh-129726).

There are a number of cases of unclosed file-like objects being deleted in CPython libraries and the test suite. This issue includes resolving those cases where the new ResourceWarning is emitted.

cc: @vstinner

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

#129726 (comment)

Linked PRs

• gh-130806: emit ResourceWarning if GzipFile unclosed #130905