diff -r d35fc6e58a70 Lib/tempfile.py
--- a/Lib/tempfile.py	Sun Dec 04 22:59:09 2016 +0100
+++ b/Lib/tempfile.py	Wed Dec 07 07:43:44 2016 -0800
@@ -447,7 +447,10 @@
 
         # Need to ensure the file is deleted on __del__
         def __del__(self):
-            self.close()
+            if not self.close_called and self.file is not None:
+                _warnings.warn('unclosed file %r' % self, ResourceWarning,
+                               stacklevel=2, source=self)
+                self.close()
 
     else:
         def close(self):
diff -r d35fc6e58a70 Lib/test/test_tempfile.py
--- a/Lib/test/test_tempfile.py	Sun Dec 04 22:59:09 2016 +0100
+++ b/Lib/test/test_tempfile.py	Wed Dec 07 07:43:44 2016 -0800
@@ -957,6 +957,14 @@
             tempfile.NamedTemporaryFile(mode=2, dir=dir)
         self.assertEqual(os.listdir(dir), [])
 
+    def test_resource_warning_on_destructor(self):
+        file = tempfile.NamedTemporaryFile()
+        with warnings.catch_warnings(record=True) as w:
+            del file
+        self.assertEqual(len(w), 1)
+        self.assertEqual(w[-1].category, ResourceWarning)
+        self.assertIn('unclosed file', str(w[-1].message))
+
     # How to test the mode and bufsize parameters?
 
 class TestSpooledTemporaryFile(BaseTestCase):
diff -r d35fc6e58a70 Lib/test/test_urllib2.py
--- a/Lib/test/test_urllib2.py	Sun Dec 04 22:59:09 2016 +0100
+++ b/Lib/test/test_urllib2.py	Wed Dec 07 07:43:44 2016 -0800
@@ -739,18 +739,18 @@
             ]:
             req = Request(url)
             req.timeout = None
-            r = h.ftp_open(req)
-            # ftp authentication not yet implemented by FTPHandler
-            self.assertEqual(h.user, user)
-            self.assertEqual(h.passwd, passwd)
-            self.assertEqual(h.host, socket.gethostbyname(host))
-            self.assertEqual(h.port, port)
-            self.assertEqual(h.dirs, dirs)
-            self.assertEqual(h.ftpwrapper.filename, filename)
-            self.assertEqual(h.ftpwrapper.filetype, type_)
-            headers = r.info()
-            self.assertEqual(headers.get("Content-type"), mimetype)
-            self.assertEqual(int(headers["Content-length"]), len(data))
+            with h.ftp_open(req) as r:
+                # ftp authentication not yet implemented by FTPHandler
+                self.assertEqual(h.user, user)
+                self.assertEqual(h.passwd, passwd)
+                self.assertEqual(h.host, socket.gethostbyname(host))
+                self.assertEqual(h.port, port)
+                self.assertEqual(h.dirs, dirs)
+                self.assertEqual(h.ftpwrapper.filename, filename)
+                self.assertEqual(h.ftpwrapper.filetype, type_)
+                headers = r.info()
+                self.assertEqual(headers.get("Content-type"), mimetype)
+                self.assertEqual(int(headers["Content-length"]), len(data))
 
     def test_file(self):
         import email.utils
@@ -1167,10 +1167,11 @@
                 try:
                     method(req, MockFile(), code, "Blah",
                            MockHeaders({"location": to_url}))
-                except urllib.error.HTTPError:
+                except urllib.error.HTTPError as e:
                     # 307 in response to POST requires user OK
                     self.assertEqual(code, 307)
                     self.assertIsNotNone(data)
+                    e.close()
                 self.assertEqual(o.req.get_full_url(), to_url)
                 try:
                     self.assertEqual(o.req.get_method(), "GET")
@@ -1206,9 +1207,10 @@
             while 1:
                 redirect(h, req, "http://example.com/")
                 count = count + 1
-        except urllib.error.HTTPError:
+        except urllib.error.HTTPError as e:
             # don't stop until max_repeats, because cookies may introduce state
             self.assertEqual(count, urllib.request.HTTPRedirectHandler.max_repeats)
+            e.close()
 
         # detect endless non-repeating chain of redirects
         req = Request(from_url, origin_req_host="example.com")
@@ -1218,9 +1220,10 @@
             while 1:
                 redirect(h, req, "http://example.com/%d" % count)
                 count = count + 1
-        except urllib.error.HTTPError:
+        except urllib.error.HTTPError as e:
             self.assertEqual(count,
                              urllib.request.HTTPRedirectHandler.max_redirections)
+            e.close()
 
     def test_invalid_redirect(self):
         from_url = "http://example.com/a.html"
@@ -1234,9 +1237,13 @@
 
         for scheme in invalid_schemes:
             invalid_url = scheme + '://' + schemeless_url
-            self.assertRaises(urllib.error.HTTPError, h.http_error_302,
-                    req, MockFile(), 302, "Security Loophole",
-                    MockHeaders({"location": invalid_url}))
+            with self.assertRaises(urllib.error.HTTPError):
+                try:
+                    h.http_error_302(req, MockFile(), 302, "Security Loophole",
+                                     MockHeaders({"location": invalid_url}))
+                except urllib.error.HTTPError as e:
+                    e.close()
+                    raise
 
         for scheme in valid_schemes:
             valid_url = scheme + '://' + schemeless_url