Issue #22384: An exception in Tkinter callback no longer crashes the program

when it is run with pythonw.exe.

Documented that Tk.report_callback_exception() is purposed to be overriden in
applications.

Lib/tkinter/__init__.py

@@ -1917,9 +1917,12 @@ def readprofile(self, baseName, className):
         if os.path.isfile(base_py):
             exec(open(base_py).read(), dir)
     def report_callback_exception(self, exc, val, tb):
-        """Internal function. It reports exception on sys.stderr."""
+        """Report callback exception on sys.stderr.
+
+        Applications may want to override this internal function, and
+        should when sys.stderr is None."""
         import traceback
-        sys.stderr.write("Exception in Tkinter callback\n")
+        print("Exception in Tkinter callback", file=sys.stderr)
         sys.last_type = exc
         sys.last_value = val
         sys.last_traceback = tb

Misc/NEWS

@@ -32,6 +32,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #22384: An exception in Tkinter callback no longer crashes the program
+  when it is run with pythonw.exe.
+
 - Issue #22168: Prevent turtle AttributeError with non-default Canvas on OS X.
 
 - Issue #21147: sqlite3 now raises an exception if the request contains a null