bpo-32207: Improve tk event exception tracebacks in IDLE. (#4703)

When tk event handling is driven by IDLE's run loop, a confusing
and distracting queue.EMPTY traceback context is no longer added
to tk event exception tracebacks.  The traceback is now the same
as when event handling is driven by user code.  Patch based on
a suggestion by Serhiy Storchaka.

Lib/idlelib/run.py

@@ -134,13 +134,17 @@ def main(del_exitfunc=False):
                     # exiting but got an extra KBI? Try again!
                     continue
             try:
-                seq, request = rpc.request_queue.get(block=True, timeout=0.05)
+                request = rpc.request_queue.get(block=True, timeout=0.05)
             except queue.Empty:
-                handle_tk_events()
-                continue
-            method, args, kwargs = request
+                request = None
+                # Issue 32207: calling handle_tk_events here adds spurious
+                # queue.Empty traceback to event handling exceptions.
+            if request:
+                seq, (method, args, kwargs) = request
                 ret = method(*args, **kwargs)
                 rpc.response_queue.put((seq, ret))
+            else:
+                handle_tk_events()
         except KeyboardInterrupt:
             if quitting:
                 exit_now = True

Misc/NEWS.d/next/IDLE/2017-12-04-15-04-43.bpo-32207.IzyAJo.rst

+Improve tk event exception tracebacks in IDLE.
+When tk event handling is driven by IDLE's run loop, a confusing
+and distracting queue.EMPTY traceback context is no longer added
+to tk event exception tracebacks.  The traceback is now the same
+as when event handling is driven by user code.  Patch based on a
+suggestion by Serhiy Storchaka.