Fixed small issue and added more information about PROTOCOL_TLS

notebook/notebookapp.py

@@ -1421,10 +1421,11 @@ class NotebookApp(JupyterApp):
             # SSL may be missing, so only import it if it's to be used
             import ssl
             # PROTOCOL_TLS selects the highest ssl/tls protocol version that both the client and
-            # server support. When PROTOCOL_TLS is not available use PROTOCOL_SSLv23
+            # server support. When PROTOCOL_TLS is not available use PROTOCOL_SSLv23.
+            # PROTOCOL_TLS is new in version 2.7.13, 3.5.3 and 3.6
             ssl_options.setdefault(
                 'ssl_version',
-                getattr('ssl', 'PROTOCOL_TLS', ssl.PROTOCOL_SSLv23)
+                getattr(ssl, 'PROTOCOL_TLS', ssl.PROTOCOL_SSLv23)
             )
             if ssl_options.get('ca_certs', False):
                 ssl_options.setdefault('cert_reqs', ssl.CERT_REQUIRED)