ENH: #1410 DataFrame.loc with Iterable

[cmp0xff]

Note str is also Iterable[HashableT] but DataFrame.loc[..., str] produces Series instead of DataFrame, so I need to shuffle the order of the overloads.

• Closes DataFrame.loc does not like Sequence[Hashable] for the columns #1410
• Tests added

[MarcoGorelli]

thanks @cmp0xff - so the main difference is

- list[HashableT]
+ Iterable[HashableT]

in the tuple case right? the rest is just moving the overloads around?

[cmp0xff]

Hi @MarcoGorelli , yes that's what I did.

After working out this, I feel that when list is allowed but tuple is not, we may try MutableSequence to replace list. lists are not covariant, which can be annoying.