On Fri, Jul 31, 2020 at 04:08:43PM -0700, Guido van Rossum wrote:
Maybe it is common in numpy and pandas to keep adding operations to the same object until it breaks, but the key and items views already implement the Set ABC, and I'd rather refrain from having them *also* implement the Sequence ABC.
+1 I'm not a huge fan of pandas' APIs, I don't think that "pandas does it this way" is something we ought to emulate.
I'm guessing that indexing by 0, if it were possible, would be a convenient idiom to implement the "first item" operation that has been requested numerous times (at least for dicts).
Indeed, that seems to be the only use-case which seems to be even remotely common. `dict.popitem` would do it, of course, but it also mutates the dict. The other simple solution is `next(iter(mydict.items()))`. The bottom line here seems to me, as far as I can tell, is that being able to fetch a key and/or value by index is of only marginal use.
Slicing would be useful to get the first N items of a huge dict without materializing the full list of items as a list object, which brought Chris B to request this in the first place.
The first request in this thread was from Hans: https://mail.python.org/archives/list/python-ideas@python.org/message/S7UMTW... He is using a dict to hold an array of columns indexed by name `{column_name: column}` and wanted to re-order and insert columns at arbitrary positions. -- Steven