On Sat, Apr 18, 2020 at 09:13:44PM +0200, Dominik Vilsmeier wrote:
>
> func(foo, **, bar) vs. func(foo, **{bar})
>
> It's still a mode switch, only the beginning and end markers have
> changed. Instead of `**,` (or `**mapping,`) we then have `**{` as the
> opening marker and instead of `)` (the parenthesis that closes the
> function call) we have `}` as the closing marker.
How do you define a mode switch?
Is a list display a mode? Is a string a mode? Is a float a mode?
In some sense, maybe, but to me the critical factor is that nobody talks
about "list mode", "string mode", let alone "float mode". Its about the
mental model.
With `func(foo, **, bar, baz, quux)` if I use `**` as a pseudo-argument,
the interpreter switches to "auto-fill" mode and everything that follows
that (until the end of the function call) has to be interpreted
according to the mode.
A few people immediately started describing this as a mode, without
prompting. I think it is a very natural way of thinking about it.
And we have no way of turning the mode off. So if there is every a
proposal to allow positional arguments to follow keyword arguments, it
won't be compatible with auto-fill mode.
With `func(foo, **{bar, baz, quux})` the mental model is closer to
ordinary argument or dict unpacking. Nobody refers to this:
func(spam, *[eggs, cheese, aardvark], hovercraft)
as "list mode" or "argument unpacking mode". It's just "unpacking a
list" or similar. No-one thinks about the interpreter entering a special
"collect list mode" even if that's what the parser actually does, in
some sense. We read the list as an entity, which then gets unpacked.
Likewise for dict unpacking: nobody thinks of `{'a': expr}` as entering
"dict mode". You just make a dict, then unpack it.
And nobody (I hope...) will think of keyword shortcut as a mode:
func(foo, **{bar, baz}, quux=1)`
It's just unpacking an autofilled set of parameter names. Not a mode at
all. And notice that there is absolutely no difficulty with some future
enhancement to allow positional arguments after keyword arguments.
--
Steven
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