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

Lib/gzip.py

@@ -245,9 +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 KI
+            try:
+                if self.myfileobj is not None:
+                    self.myfileobj.close()
+            finally:
+                self.fileobj = None
+            raise
     @property
     def mtime(self):
         """Last modification time read from stream, or None"""

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