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Negative indices have an implied ”len(list)” in front of them. They can be seen as an application of the idea of half-open intervals (0 <= i < len(list)), so it
by nemetroid 6y ago
Negative indices have an implied ”len(list)” in front of them. They can be seen as an application of the idea of half-open intervals (0 <= i < len(list)), so it makes sense that they’re not symmetrical.
- naniwaduni 6y agoIs this sensible, or is it an unprincipled ad-hoc justification for a feature that happens to be useful? Or another way: Is this more reasonable than, say, implicitly taking indices mod len(list)? How about implicitly flooring indices? If so, why?
- nemetroid 6y agoI'm not sure on what principles you'd make a principled justification. My most common use of negative indices is for slicing the end of the list, in which context the interpretation similar to len(list) makes sense. E.g., list[:-2] does what you'd expect (the same as list[2:], except from the other end). > implicitly taking indices mod len(list)? Isn't this doing that (plus some bounds checking)? -1 mod 4 evaluates to 3. > implicitly flooring indices? Not sure I understand what this means.