Why are slice and range upper-bound exclusive?
language-design, python, slice
Solution
The documentation implies this has a few useful properties:
word[:2] # The first two characters
word[2:] # Everything except the first two characters
Here’s a useful invariant of slice operations: `s[:i] + s[i:]` equals `s`.
For non-negative indices, the length of a slice is the difference of the indices, if both are within bounds. For example, the length of `word[1:3]` is `2`.
I think we can assume that the range functions act the same for consistency.
Problem
I know that when I use `range([start], stop[, step])` or `slice([start], stop[, step])`, the `stop` value is not included in the range or slice. But why does it work this way? Is it so that e.g. a `range(0, x)` or `range(x)` will contain `x` many elements? Is it for parallelism with the C for loop idiom, i.e. so that `for i in range(start, stop):` superficially resembles `for (i = start ; i < stop; i++) {`? See also Loop backwards using indices for a case study: setting the `stop` and `step` values properly can be a bit tricky when trying to get values in descending order.