@ Terry J. Reedy

If it is working for you it doesn't necessarily mean that it is working
for mankind in general.

I traced down the problem to the OS X- implementation of Idle in general
and submitted an inquiry to the general python list as you suggested.
The feedback was null- nada- niente. But in the meantime I received a
nice bunch of Spam instead.

http://mail.python.org/pipermail/python-list/2008-August/504330.html

I believe the original poster has a French keyboard and seems to have 
similar problems. The problem is that Idle seems to ignore the
international local keyboard setting. And as we do have two significant
letters ("#" and "'") at the keyboard position where you have the "\"
Idle seems to filter the entry of a backslash.

@ marc 67
HTH

Cheers
Ulf