I think there definitely should be a more obvious way to do this (specifically the first and last keys/values/items of a dictionary — I'm ambivalent about the others, since they won't always be fast, as discussed). An anti-pattern you see quite often on Stack Overflow to get the first key of a dictionary is something like the following:

        first_key = list(mydict.keys())[0]

Whereas obviously, a much better way (especially if it's a very large dictionary) is to do:

        first_key = next(iter(mydict))

[Christopher Barker]
I'll leave it exercise for the reader to find that thead

For reference, the (very long) previous thread is here: https://mail.python.org/archives/list/python-ideas@python.org/thread/S7UMTWK65X6BJDYZ3SSU7I7HOIASDMMJ/.

[Inada Naoki]
I think we can add `itertools.first()` for this idiom, and
`itertools.last()` for `next(iter(reversed(x)))` idiom.

I like this idea, a lot. Another possibility I've been wondering about was whether several methods should be added to the dict interface:
  • dict.first_key = lambda self: next(iter(self))
  • dict.first_val = lambda self: next(iter(self.values()))
  • dict.first_item = lambda self: next(iter(self.items()))
  • dict.last_key = lambda self: next(reversed(self))
  • dict.last_val = lambda self: next(reversed(self.values()))
  • dict.last_item = lambda self: next(reversed(self.items()))
But I think I like a lot more the idea of adding general ways of doing these things to itertools.

Best,
Alex

On 5 Oct 2021, at 05:30, Christopher Barker <pythonchb@gmail.com> wrote:


On Mon, Oct 4, 2021 at 5:46 PM Erik Demaine <edemaine@mit.edu> wrote:
Have folks thought about allowing indexing dictionary views as in the
following code, where d is a dict object?

d.keys()[0]
d.keys()[-1]
d.values()[0]
d.values()[-1]
d.items()[0]
d.items()[-1]  # item that would be returned by d.popitem()

since dicts were made order-preserving, indexing the keys, items, etc does make some sense.


> I've also often wanted to get an arbitrary item/key from a dictionary, and

This is indeed one of the use cases identified.

I found some related discussion in
https://mail.python.org/archives/list/python-ideas@python.org/thread/QVTGZD6USSC34D4IJG76UPKZRXBBB4MM/
but not this exact idea.

That's a pretty different idea but this exact idea has been discussed on this list relatively recently. I still like it, but there wan't much general support.

I'll leave it exercise for the read to find that thead, but it is there, and I suggest you look for it if you want to further pursue this idea.

-CHB


--
Christopher Barker, PhD (Chris)

Python Language Consulting
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