[Python-ideas] Syntactic sugar to declare partial functions

[Neil Girdhar]

By the way, these are not "partial functions", and shouldn't be called 
that.  These are "partial function applications".

On Saturday, August 4, 2018 at 12:03:50 PM UTC-4, Fabrizio Messina wrote:
>
>  
> Hello, I would like to propose a new method to create a partial function.
>
> At the moment we have to load the *partial* function from the *functool* 
> library, and apply it to an existing function, e.g. 
>
> from functools import partial
>
>
> def add(x: int, y: int) -> int:
>     return x + y
>
>
> add_2 = partial(add, 2)
>
>
>
> While partial expose the mechanism excellently its instantiation method 
> is, at times, not very friendly, I would like to propose a syntactic sugar 
> to create partial functions, in the case you create a partial function 
> using *curly braces*:
>
>
> def add(x: int, y: int) -> int:
>     return x + y
>
> add_2 = add{2}
>
>
> At the moment this causes SyntaxError so the change is retro-compatible.
>
> In the case of key word arguments we could have:
>
> sort_by_x = sort{key=lambda element: element.x}
>
>
> That could be good as it would be an easy way to pre-load functions 
> without having to eagerly compute it, but without needing to pass the 
> entire function parameters to to other scopes.
>
>
> # prepare the function
> get_sorted_users: Callable[[], Iterator[User]] = sort{users, key=lambda 
> user: user.creation_date}
>
> # continue with job at hand
> ...
>
> # some where else, maybe another process
> sorted_users = list(get_sorted_users())
>
>
>
> Even create a factory method on the fly:
> @dataclass
> class Product:
>     name: str
>     category: Category
>     price: Decimal
>
>
> smartphone_factory = Product{category=smartphone_category}
>
>
>
> Now all this can already be done with partial, but adding this syntactic 
> sugar would reduce the perception of `partial` as an advanced feature, 
> alleviating the use of closures created only for the sake of avoiding an 
> explicit partial.
>
> In my opinion this syntactic sugar has a lot of potential adoption seen 
> the general interest in functional programming.
>
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