Fix some Python 3.8 related issues

nilmdb/server/serverutil.py

@@ -6,6 +6,7 @@ import sys
 import json
 import decorator
 import functools
+import threading
 
 import cherrypy
 
@@ -178,6 +179,19 @@ def cherrypy_patch_exit():
             os._exit = real_exit
     bus.exit = functools.partial(patched_exit, bus.exit)
 
+    # A behavior change in Python 3.8 means that some thread exceptions,
+    # derived from SystemExit, now print tracebacks where they didn't
+    # used to: https://bugs.python.org/issue1230540
+    # Install a thread exception hook that ignores CherryPyExit;
+    # to make this match the behavior where we didn't set
+    # threading.excepthook, we also need to ignore SystemExit.
+    def hook(args):
+        if args.exc_type == CherryPyExit or args.exc_type == SystemExit:
+            return
+        sys.excepthook(args.exc_type, args.exc_value,
+                       args.exc_traceback) # pragma: no cover
+    threading.excepthook = hook
+
 
 # Start/stop CherryPy standalone server
 def cherrypy_start(blocking=False, event=False):

nilmdb/utils/timestamper.py

@@ -26,7 +26,9 @@ class Timestamper():
                 return b""
             if line[0:1] == b'#':
                 continue
-            break
+            # For some reason, coverage on python 3.8 reports that
+            # we never hit this break, even though we definitely do.
+            break # pragma: no cover
         try:
             return next(self.ts_iter) + line
         except StopIteration: