When using slicing for a sequence object, with a user defined __getslice__ function, the arguments to __getslice__ are changed. This does not happen when __getslice__is called directly. Attached is some code that demonstrates the problem. I checked it on various versions, including my "Python 2.5.1 (r251:54863, May 2 2007, 16:56:35)", on my Ubuntu machine. Although __getslice__ is deprecated, there is still usage of the function, and a fix would be useful.
Unfortunately, this is a feature, not a bug. The relevant code is in Python/ceval.c apply_slice(). Calls to s[a:b] get pre-processed before being handed-off to s.__getslice__. This behavior has been around so long, that it is almost certain that there is a good body of existing code that relies on the behavior.
