Rename keyword argument reverse to ascending for sorting methods

[zundertj]

Problem description

Summary

In Polars, the sorting methods (on expressions/series/dataframes) have a keyword argument named reverse. I propose to change this name to ascending.

Rationale

The issue I have with reverse is that it does not tell me what "non reverse" / "normal" is. The docstring on for example DataFrame.sort also acknowledges this, because it says:

    reverse

        Reverse/descending sort.

I.e., reverse=descending, so non-reverse=ascending. You wouldn't know from the parameter name itself. Docs are good, but proper argument naming is better.

Pandas does use ascending. Pandas consistency is not a goal, but I feel Pandas has the better naming here.

PyArrow opts for the name order, and asks for a string to be passed in (ascending or descending). See for example array_sort_indices. As long as we can imagine having only two orderings, a bool is easier than a string imo, so I like the Pandas approach more.

Moreover, I don't see a drawback in adopting this terminology, other than that we have to do a one-time breaking release.

[zundertj]

(not knowing the Rust code that well) We could set the default for ascending to True, or if we go with descending to False, both will achieve ascending by default. Reason I picked ascending and not descending is that is what Pandas does. Probably a matter of taste.

[ritchie46]

Yes, I have been thinking about this one as well. I think we should name it to descending so that the default in rust remains in ascending order.

If we do this we need to do both rust and python at once.