Backport PR #336: handle classes having been torn down in atexit

Author: takluyver

jupyter_client/channels.py

@@ -80,7 +80,10 @@ def __init__(self, context=None, session=None, address=None):
     @staticmethod
     @atexit.register
     def _notice_exit():
-        HBChannel._exiting = True
+        # Class definitions can be torn down during interpreter shutdown.
+        # We only need to set _exiting flag if this hasn't happened.
+        if HBChannel is not None:
+            HBChannel._exiting = True
 
     def _create_socket(self):
         if self.socket is not None:

jupyter_client/threaded.py

@@ -151,7 +151,10 @@ def __init__(self, loop):
     @staticmethod
     @atexit.register
     def _notice_exit():
-        IOLoopThread._exiting = True
+        # Class definitions can be torn down during interpreter shutdown.
+        # We only need to set _exiting flag if this hasn't happened.
+        if IOLoopThread is not None:
+            IOLoopThread._exiting = True
 
     def run(self):
         """Run my loop, ignoring EINTR events in the poller"""