bpo-33034: Improve exception message when cast fails for {Parse,Split}Result.port (GH-6078)

Lib/test/test_urlparse.py

@@ -936,6 +936,16 @@ class UrlParseTestCase(unittest.TestCase):
         self.assertEqual(p2.scheme, 'tel')
         self.assertEqual(p2.path, '+31641044153')
 
+    def test_port_casting_failure_message(self):
+        message = "Port could not be cast to integer value as 'oracle'"
+        p1 = urllib.parse.urlparse('http://Server=sde; Service=sde:oracle')
+        with self.assertRaisesRegex(ValueError, message):
+            p1.port
+
+        p2 = urllib.parse.urlsplit('http://Server=sde; Service=sde:oracle')
+        with self.assertRaisesRegex(ValueError, message):
+            p2.port
+
     def test_telurl_params(self):
         p1 = urllib.parse.urlparse('tel:123-4;phone-context=+1-650-516')
         self.assertEqual(p1.scheme, 'tel')

Lib/urllib/parse.py

@@ -166,7 +166,11 @@ class _NetlocResultMixinBase(object):
     def port(self):
         port = self._hostinfo[1]
         if port is not None:
-            port = int(port, 10)
+            try:
+                port = int(port, 10)
+            except ValueError:
+                message = f'Port could not be cast to integer value as {port!r}'
+                raise ValueError(message) from None
             if not ( 0 <= port <= 65535):
                 raise ValueError("Port out of range 0-65535")
         return port

Misc/NEWS.d/next/Library/2018-03-11-08-44-12.bpo-33034.bpb23d.rst

@@ -0,0 +1,3 @@
+Providing an explicit error message when casting the port property to anything 
+that is not an integer value using ``urlparse()`` and ``urlsplit()``.
+Patch by Matt Eaton.