This is because list.index() has start and stop parameters, and L.index(x) is equivalent to L.index(x, 0, len(L)). In list.count() and list.remove() the limit is dynamic during iteration, but in list.index() it is specified by arguments before iterating. It is possible to make the limit static in list.count() and list.remove() or to make it floating if stop is absent or negative in list.index(), but this will complicate and slow down the code without good reason. I suggest to close this issue as "wont fix".