This issue is about formatting a value into an error message.
#1182143 is about adding values that have already been formatted into an
error message to the resulting exception object.  If this suggestion
were implemented, then IndexError would be added to the exceptions
covered by #1182143

Patches to mailing lists tend to get lost.  Thank you for finding
Bjourne's. I have invited him (at the email then given) to update it and
attach it here.