ENH: GH12034 RangeIndex.__floordiv__ returns RangeIndex if possible

[kawochen]

xref #12034

[kawochen]

Not sure if I should always return RangeIndex when length < 2.

[jreback]

@kawochen I had the same thoughts for n=0/1 for the default constructor for a NDFrame, but thought its more consistent to always get a RangeIndex. Ideally would do the same if at all possible.

[jreback]

pls add this issue number to the whatsnew note as well.

[jreback]

shouldn't you just have exact=True here?

[kawochen]

For len(self) == 1 and len(self) == 0 the equivalent classes are particularly large, and it doesn't matter which representatives to return. e.g. you could always return RangeIndex() for len(self) == 0 or leave _start unchanged. And since when len(self) == 1, step // div could be 0, I couldn't treat all cases the same. The choice of step and stop is arbitrary so I had exact=False.

[kawochen]

oh I just looked at assert_index_equal, so it defers to Index.equals -- I will change it to exact=True

[jreback]

the exact defaults to equiv which means Int64Index/RangeIndex can be equivalent. exact=True mean they must be exactly the same

[jreback]

ping when green

[kawochen]

updated

[jreback]

merged via 8e29361

thanks!