gh-131492: gh-131461: handle exceptions in GzipFile constructor while owning resources

Lib/gzip.py

@@ -245,8 +245,17 @@ def __init__(self, filename=None, mode=None,
 
         self.fileobj = fileobj
 
-        if self.mode == WRITE:
-            self._write_gzip_header(compresslevel)
+        try:
+            if self.mode == WRITE:
+                self._write_gzip_header(compresslevel)
+        except BaseException:
+            # Avoid a ResourceWarning if the write fails, eg read-only file or KeyboardInterrupt
+            try:
+                if self.myfileobj is not None:
+                    self.myfileobj.close()
+            finally:
+                self.fileobj = None
+            raise
 
     @property
     def mtime(self):

Lib/test/test_tarfile.py

@@ -19,6 +19,7 @@
 from test import support
 from test.support import os_helper
 from test.support import script_helper
+from test.support import warnings_helper
 
 # Check for our compression modules.
 try:
@@ -1638,10 +1639,13 @@ def write(self, data):
                         raise exctype
 
             f = BadFile()
-            with self.assertRaises(exctype):
-                tar = tarfile.open(tmpname, self.mode, fileobj=f,
-                                   format=tarfile.PAX_FORMAT,
-                                   pax_headers={'non': 'empty'})
+            with (
+                warnings_helper.check_no_resource_warning(),
+                self.assertRaises(exctype),
+            ):
+                tarfile.open(tmpname, self.mode, fileobj=f,
+                             format=tarfile.PAX_FORMAT,
+                             pax_headers={'non': 'empty'})
             self.assertFalse(f.closed)
 
     def test_missing_fileobj(self):

Misc/NEWS.d/next/Library/2025-03-19-14-36-54.gh-issue-131461.uDUmdY.rst

@@ -0,0 +1 @@
+Fix :exc:`ResourceWarning` when constructing a :class:`gzip.GzipFile` in write mode with a broken file object.