Short Form prevents the Python shell from printing out giant piles of text.
It is a hack that ties into the display system. When you are working with a multi-megabyte text file, referenced under the name txt, which takes 10 minutes to be printed in full (if you accidentally type ‘>>> txt’) it’s really nice to have this.
Besides actually turning it off, it can be evaded by using print or even sys.stdout.write itself. ShortForm is only used when an object is repr’ed and printed.