[Python-ideas] Syntactic sugar to declare partial functions

[Daniel.]

That's an awesome library! Congratulation for doing this and thanks for
sharing!

Em sáb, 4 de ago de 2018 às 13:42, Robert Vanden Eynde <robertve92 at gmail.com>
escreveu:

> The funcoperators lib on pypi does exactly that:
>
> from funcoperators import partially
>
> @partially
> def add(x: int, y: int) -> int:
>     return x + y
>
> add_2 = add[2]
>
> @partiallymulti
> def stuff(x,y,z):
>     return x - y + 2*z
>
> sort = partially(sorted)
> sort_by_x = sort.key(key=lambda element: element.x)
>
> The ".key" means "give a keyword argument".
> The ".val" or [] gives a positional argument.
> The ".part" accept positional and keyword arguments.
>
> Le sam. 4 août 2018 à 18:03, Fabrizio Messina <zauddelig at gmail.com> a
> écrit :
>
>>
>> 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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>>
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