> On Apr 16, 2020, at 12:05, Dominik Vilsmeier <[email protected]> wrote:
>
> I'm not sure if this is doable from the compiler perspective, but what
> about allowing tuples after `**` unpacking:
>
> requests.post(url, **(data, params))
>
> # similar to
> requests.post(url, data=data, params=params)
Is this actually a tuple? So the items can be any expression at all? Then
what’s the keyword for, say, `requests.post(url, **(data, timeout*2))`?
Also, could you use **tuple in other contexts where **unpacking is allowed,
like dict displays, or only in calls?
If we’re going to build on ** unpacking, maybe instead of coming up with
special syntax that works everywhere **unpacking does, or that only works in
some places **unpacking does, it would be simpler/cleaner to come up with
special syntax just for dict displays—which automatically gives you the ability
to **unpack in calls and anywhere else?
Here’s a straw man. A one-liner grammar change is all you need, and restricting
it to just identifiers is easy:
key_datum ::= expression ":" expression | "**" or_expr | ":" identifier
And the semantics of the new third form would be that the key is the name of
the identifier as a string and the value is the value of the identifier as an
expression.
And here’s what it looks like:
requests.post(url, **{:data, :params})
The obvious way to mix normal and magic keywords just works; you can of course
write this:
requests.post(url, headers=makeheaders(), **{:data, :params})
… but if headers has to come after data for some reason you can do this:
requests.post(url, **{:data, "headers": makeheaders(), :params})
… or, if you prefer, this:
requests.post(url, **{:data}, headers=makeheaders(), **{:params})
… because we’re just using the already-working, well-understood rules for
**unpacking.
And it can also be used outside of calls:
params = {:name, :email, "phone": formatphone(phone)}
request.post(url, json=params)
… which also means you could refactor a really hairy call in an obvious way:
kw = { :data, "headers": makeheaders(), :params }
requests.post(url, **kw)
Extending it beyond identifiers might be useful, but there are enough potential
problems and questions (e.g., is the name of :spam.eggs “spam.eggs” or “eggs”?)
that it would almost certainly be worth putting off to a future version after
people have gotten experience with the basic feature.
I’m not sure if I like this syntax, but I do like it better than the magic *
separator syntax and the magic **-unpack-a-tuple syntax. (And I like the
overall idea in this thread if someone can come up with good enough syntax.)
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