DEPR: DataFrame.__getitem__[str] sometimes slices on index

[jbrockmendel]

xref #31334, #9595

• This is a tiny corner case, at least as measured by tests cases (2 tests reach this)
• With this removed, the __getitem__ API becomes much simpler to describe: "DataFrame.getitem` is always column-based"

[jorisvandenbossche]

@jbrockmendel Can you be more clear or specific in the description of the issue? And give some examples of the behaviour you want to deprecate?

For example: do you want to deprecate all slicing in __getitem__, or only the slicing with a single string? Because in #31334, you never mentioned it is only about "single string" slicing, while the title here suggest otherwise.

With this removed, the getitem API becomes much simpler to describe: "DataFrame.getitem` is always column-based"

Assuming you only mean "partial datetime string slicing with a single string", note that __getitem__ still does row-based access (normal slicing, boolean masks). So the "getitem is always column-based" is a bit confusing. I suppose you mean: when passing a single, scalar label, it is always column-based.