Dict key=>value to array in comprehension

General Usage
1

I’m trying to build a Cmd from the kwargs of a function. Basically, I want to turn eg foo("some_option"; opt1 = "thing", opt2="other_thing") into run(`my_cli some_option --opt1 thing --opt2 other_thing`). Cmd() can take a vector of strings, so I’m trying to use a comprehension to convert kwargs... into such a vector.

Basic function signature is

function foo(c1; kwargs...)
    c = ["my_cli", c1]
    append!(c, <something>)
    run(Cmd(c))
end

Where <something> is currently Iterators.flatten(("--" * string(k), string(v)) for (k,v) in pairs(kwargs))). So basically I’m making tuples of key=>value and then using Iterators.flatten to press them into a sequential vectorz. This works, but I was wondering if this is the best* approach? Other things I tried that didn’t work:

[("--" * string(k), string(v))... for (k,v) in pairs(kwargs)]
["--" * string(k), string(v) for (k,v) in pairs(kwargs)]

* I realize “best” is quite subjective, and perhaps I should be fine with the flatten approach, but it feels somehow more verbose than I was expecting. Then again, this is exactly what flatten is for, so…

2

It can be helpful to lean on command interpolation as much as possible instead of worrying about strings.

If you interpolate an iterable into a cmd, it’ll automatically “splat” out the contents with correct quoting and such:

julia> function foo(c1; kwargs...)
           args = Iterators.flatten((string("--", k), v) for (k,v) in pairs(kwargs))
           `$c1 $args`
       end
foo (generic function with 1 method)

julia> foo(`echo`; a = 1, b = 2)
`echo --a 1 --b 2`

Leaning on the pretty printing’s underlines can help you see that it’s putting quotes in the right places:

image

2 Likes
3

That answers a slightly different question, but nice to know! That wouldn’t have occurred to me. That said, my actual use-case is slightly more complicated, since, at least for the keys, I need replace _ with - since I can’t do eg foo(blah; my-opt = "bar"). But I can do this at least for the value :thinking:

4 
   function foo(c1; kwargs...)
       args = Iterators.flatten((replace(string("--", k), '_'=>'-'), v) for (k,v) in pairs(kwargs))
       `$c1 $args`
   end
1 Like