On Thu, Jul 30, 2020 at 08:52:34AM -0700, Christopher Barker wrote:
> The point being that dicts are now ordered, so maybe it makes sense to add
> some operations that make it natural and easy to work with them in an
> ordered way -- you know, like slicing :-)
Dicts are not sequences and cannot support ordering operations like
insert, sort, prepend, reverse or slice assignment. They merely preserve
insertion order.
You can't insert a key in a specific position. If I have this dict:
mydict = {'a': 1, 'c': 3, 'd': 4, 'e': 5}
I can't insert 'b':2 between keys 'a' and 'c', except by creating a new
dict. Nor can I sort the keys, or reverse them, except by putting them
into a list and sorting or reversing the list, and only then putting
them into a dict.
We could read the key and/or value at index N, that is straight forward
if we can decide on a colour of the bike shed. But I don't believe that
there is an straight forward way of replacing the key at index N, or of
inserting keys, or swapping them, or directly changing their order.
Dicts are, sort of, like a stack: you can "insert" (append) new keys at
the end, but not in the middle.
So let's please stop over-generalising by saying dicts are "ordered"
without the qualifier that they only preserve insertion order, just like
collections.OrderedDict.
The minimal API we could support would be a getter that returns the key
at index N. Once you have the key, you can get or set the value. So all
we really need is that one single getter. Anything else is gravy.
dict.getkey(n) # returns the key at index n by insertion order
I wouldn't object to:
dict.getitem(n) # returns (key, value) at index n
since it's hardly more trouble to return both the key and the value at
the same time. But more than that seems difficult to justify, and
supporting slices seems like overkill. You can always get them with a
comprehension:
[mydict.getkey(n) for n in range(3, 49, 7)]
--
Steven
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