Have you ever written code that looks like this:

if isinstance(d.index, MultiIndex): results = [] for l in d.index.levels: for x in baz(l): results.append(foo) elif isinstance(d.index, Index): for x in d.index: foo 

I've had to special case the handling of index vs. multindex several times in the past.
Conceptually, I should be able to treat index as a private case of MultIndex
with nlevels =1, and supporting that in the API would make things nicer.

Edit by @cpcloud:
Tasks :

API Unification

Method unification is relatively simple:

• Index.from_tuples and Index.from_arrays are just MultiIndex.from_tuples and MultiIndex.from_arrays moved to classmethods of Index.
• droplevel, ` just raises on Index (right? what would it mean?): API: implement droplevels() for flat index #21115
• has_duplicates is straightforward
• truncate should be equivalent to slicing
• reorder_levels raises if not level=0 or name of index
• equal_levels - straightforward
• levshape - (len(ind),)
• sortorder - None
• get_loc_level - I think meaningless with tuple, raises whatever if not 0 or index name
• is_lexsorted - doesn't need to change
• is_lexosrted_tuple - doesn't need to change
• is_monotonic_*
• lexsort_depth - doesn't need to be changed at all
• searchsorted
• repeat
• levels and labels property for Index - question on whether it should be sorted.
• change to rename behavior: Index will accept either string or single-element list; MI continues to handle only list