gh-76646: Fix proxy_bypass_registry trailing semicolon on Windows

Lib/test/test_urllib.py

@@ -1,7 +1,8 @@
 """Regression tests for what was in Python 2's "urllib" module"""
 
 import urllib.parse
-import urllib.request
+import urllib.request 
+import _proxy_bypass_winreg_override as proxy_bypass_winreg
 import urllib.error
 import http.client
 import email.message
@@ -1686,6 +1687,14 @@ def test_with_method_arg(self):
         request.method = 'HEAD'
         self.assertEqual(request.get_method(), 'HEAD')
 
+class ProxyBypassRegistryTests(unittest.TestCase):
+    def test_proxy_bypass_registry_trailing_semicolon(self):
+        fake_proxy_override = "localhost;*.example.com;"
+
+        # Directly test the internal function
+        self.assertFalse(proxy_bypass_winreg("notmatching.com", fake_proxy_override))
+        self.assertTrue(proxy_bypass_winreg("localhost", fake_proxy_override))
+        self.assertTrue(proxy_bypass_winreg("sub.example.com", fake_proxy_override))
 
 if __name__ == '__main__':
     unittest.main()

Lib/urllib/request.py

@@ -1996,29 +1996,34 @@ def ip2num(ipAddr):
 
 
 # Same as _proxy_bypass_macosx_sysconf, testable on all platforms
-def _proxy_bypass_winreg_override(host, override):
+def _proxy_bypass_winreg_override(host, proxy_override):
     """Return True if the host should bypass the proxy server.
 
     The proxy override list is obtained from the Windows
     Internet settings proxy override registry value.
 
     An example of a proxy override value is:
-    "www.example.com;*.example.net; 192.168.0.1"
+    "www.example.com;*.example.net;192.168.0.1"
     """
     from fnmatch import fnmatch
 
     host, _ = _splitport(host)
-    proxy_override = override.split(';')
+
+    proxy_override = proxy_override.split(';')
     for test in proxy_override:
         test = test.strip()
+        if not test:
+            continue
+
         # "<local>" should bypass the proxy server for all intranet addresses
         if test == '<local>':
             if '.' not in host:
                 return True
         elif fnmatch(host, test):
             return True
-    return False
 
+    return False
+
 
 if sys.platform == 'darwin':
     from _scproxy import _get_proxy_settings, _get_proxies

Misc/NEWS.d/next/Windows/2025-08-27-15-59-56.gh-issue-76646.88J2hZ.rst

@@ -0,0 +1 @@
+.. gh-76646: Fix proxy_bypass_registry on Windows when ProxyOverride ends with a trailing semicolon. Empty entries are now ignored.