Import warnings eagerly in zipfile and simplify the tests

Author: brittanyrey

Lib/test/test_zipfile/test_core.py

@@ -4095,28 +4095,13 @@ def test_garbage_collection(self):
             zf.close()
             del zf
 
-    def test_garbage_collection_closes_when_warning_fails(self):
-        buf = io.BytesIO()
-        zf = zipfile.ZipFile(buf, "w")
-        zf.writestr("f.txt", b"data")
-        with warnings.catch_warnings(), catch_unraisable_exception() as cm:
-            warnings.simplefilter("error", ResourceWarning)
+        # ResourceWarning escalated to an error is reported as unraisable.
+        zf = zipfile.ZipFile(io.BytesIO(), "w")
+        with (warnings.catch_warnings(action="error", category=ResourceWarning),
+              catch_unraisable_exception() as cm):
             del zf
             gc_collect()
-            self.assertIsInstance(cm.unraisable.exc_value, ResourceWarning)
-        with zipfile.ZipFile(buf) as zf:
-            self.assertEqual(zf.namelist(), ["f.txt"])
-
-    @requires_subprocess()
-    def test_unclosed_at_shutdown(self):
-        self.addCleanup(unlink, TESTFN)
-        script_helper.assert_python_ok("-c", f"""if 1:
-            import zipfile
-            zf = zipfile.ZipFile({TESTFN!r}, "w")
-            zf.writestr("f.txt", b"data")
-        """)
-        with zipfile.ZipFile(TESTFN) as zf:
-            self.assertEqual(zf.namelist(), ["f.txt"])
+            self.assertIs(cm.unraisable.exc_type, ResourceWarning)
 
     def test_unsupported_version(self):
         # File has an extract_version of 120

Lib/zipfile/__init__.py

@@ -12,7 +12,7 @@
 import sys
 import threading
 import time
-lazy import warnings
+import warnings  # must stay eager to support finalization
 
 try:
     import zlib # We may need its compression method
@@ -2650,14 +2650,10 @@ def __del__(self):
         """Call the "close()" method in case the user forgot."""
         # gh-81954: Warn if writable ZipFile is implicitly closed.
         # GC cleanup order is non-deterministic and can result in data loss.
-        try:
-            # Wrap within a try to ensure the file is closed even if the
-            # warnings module is unable to load during finalization.
-            if self.fp is not None and self.mode in ('w', 'x', 'a'):
-                warnings.warn(f"unclosed ZipFile {self!r}",
-                              ResourceWarning, source=self, stacklevel=2)
-        finally:
-            self.close()
+        if self.fp is not None and self.mode in ('w', 'x', 'a'):
+            warnings.warn(f"unclosed ZipFile {self!r}",
+                          ResourceWarning, source=self, stacklevel=2)
+        self.close()
 
     def close(self):
         """Close the file, and for mode 'w', 'x' and 'a' write the ending

Misc/NEWS.d/next/Library/2026-10-14-14-47-05.gh-issue-81954.KvM0gY.rst

@@ -1,3 +1,4 @@
-Fix data loss when a writable :class:`zipfile.ZipFile` that was never closed
-is finalized during interpreter shutdown: :meth:`~zipfile.ZipFile.close` is
-now called even if emitting the :exc:`ResourceWarning` fails.
+:mod:`zipfile` now imports :mod:`warnings` eagerly so that a writable
+:class:`~zipfile.ZipFile` left unclosed at interpreter shutdown can emit its
+:exc:`ResourceWarning` and be closed instead of failing with an
+:exc:`ImportError`.