>> With the patch, the deletion succeeded even if you get a MemoryError. The bytearray object is consistent. It's just that its buffer could be smaller (it wastes memory).

>I think intuitively I'd expect the object to be unmodified 
>if there is any error.

It would be possible to have a fully atomic operation, but it would kill performances: you have to allocate a temporary buffer to store the removed bytes. I prefer to not kill performances for a very rare case.