tornado 6 compatibility

.travis.yml

@@ -51,6 +51,7 @@ before_install:
 
 install:
     - pip install --pre .[test]
+    - pip freeze
     - wget https://github.com/jgm/pandoc/releases/download/1.19.1/pandoc-1.19.1-1-amd64.deb && sudo dpkg -i pandoc-1.19.1-1-amd64.deb
 
 

notebook/base/zmqhandlers.py

@@ -172,7 +172,7 @@ def open(self, *args, **kwargs):
 
     def send_ping(self):
         """send a ping to keep the websocket alive"""
-        if self.stream.closed() and self.ping_callback is not None:
+        if self.ws_connection is None and self.ping_callback is not None:
             self.ping_callback.stop()
             return
 
@@ -237,7 +237,7 @@ def _reserialize_reply(self, msg_or_list, channel=None):
     def _on_zmq_reply(self, stream, msg_list):
         # Sometimes this gets triggered when the on_close method is scheduled in the
         # eventloop but hasn't been called.
-        if self.stream.closed() or stream.closed():
+        if self.ws_connection is None or stream.closed():
             self.log.warning("zmq message arrived on closed channel")
             self.close()
             return

setup.py

@@ -98,7 +98,7 @@
     zip_safe = False,
     install_requires = [
         'jinja2',
-        'tornado>=4, <6',
+        'tornado>=4.1',
         # pyzmq>=17 is not technically necessary,
         # but hopefully avoids incompatibilities with Tornado 5. April 2018
         'pyzmq>=17',