Issue #20262: Warnings are raised now when duplicate names are added in the

ZIP file or too long ZIP file comment is truncated.

Lib/test/test_zipfile.py

@@ -646,7 +646,7 @@ class PyZipFileTests(unittest.TestCase):
             self.assertTrue('SyntaxError' not in reportStr)
 
             # then check that the filter works on individual files
-            with captured_stdout() as reportSIO:
+            with captured_stdout() as reportSIO, self.assertWarns(UserWarning):
                 zipfp.writepy(packagedir, filterfunc=lambda fn:
                                                      'bad' not in fn)
             reportStr = reportSIO.getvalue()
@@ -896,7 +896,9 @@ class OtherTests(unittest.TestCase):
         # Create the ZIP archive
         with zipfile.ZipFile(TESTFN2, "w", zipfile.ZIP_STORED) as zipfp:
             zipfp.writestr("name", "foo")
+            with self.assertWarns(UserWarning):
                 zipfp.writestr("name", "bar")
+            self.assertEqual(zipfp.namelist(), ["name"] * 2)
 
         with zipfile.ZipFile(TESTFN2, "r") as zipfp:
             infos = zipfp.infolist()
@@ -1213,6 +1215,7 @@ class OtherTests(unittest.TestCase):
 
         # check a comment that is too long is truncated
         with zipfile.ZipFile(TESTFN, mode="w") as zipf:
+            with self.assertWarns(UserWarning):
                 zipf.comment = comment2 + b'oops'
             zipf.writestr("foo.txt", "O, for a Muse of Fire!")
         with zipfile.ZipFile(TESTFN, mode="r") as zipfr:

Lib/zipfile.py

@@ -1104,10 +1104,10 @@ class ZipFile:
         if not isinstance(comment, bytes):
             raise TypeError("comment: expected bytes, got %s" % type(comment))
         # check for valid comment length
-        if len(comment) >= ZIP_MAX_COMMENT:
+        if len(comment) > ZIP_MAX_COMMENT:
-            if self.debug:
+            import warnings
-                print('Archive comment is too long; truncating to %d bytes'
+            warnings.warn('Archive comment is too long; truncating to %d bytes'
-                      % ZIP_MAX_COMMENT)
+                          % ZIP_MAX_COMMENT, stacklevel=2)
             comment = comment[:ZIP_MAX_COMMENT]
         self._comment = comment
         self._didModify = True
@@ -1296,8 +1296,8 @@ class ZipFile:
     def _writecheck(self, zinfo):
         """Check for errors before writing a file to the archive."""
         if zinfo.filename in self.NameToInfo:
-            if self.debug:      # Warning for duplicate names
+            import warnings
-                print("Duplicate name:", zinfo.filename)
+            warnings.warn('Duplicate name: %r' % zinfo.filename, stacklevel=3)
         if self.mode not in ("w", "a"):
             raise RuntimeError('write() requires mode "w" or "a"')
         if not self.fp:

Misc/NEWS

@@ -25,6 +25,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #20262: Warnings are raised now when duplicate names are added in the
+  ZIP file or too long ZIP file comment is truncated.
+
 - Issue #20165: The unittest module no longer considers tests marked with
   @expectedFailure successful if they pass.