PEP-646 question: unpacking into single Generic parameter
Hello, first of all, thanks for working on variadic generics! I look forward to them. My question: all the examples in https://www.python.org/dev/peps/pep-0646/ unpack into variadic arguments. But can I write code like this? ``` Ts = TypeVarTuple("Ts") def enumerate_args(f: Callable[[*Tuple[int, Ts]]], *args: *Ts): f(*enumerate(args)) ``` In particular I'm talking about the `*Tuple[int, Ts]` syntax. All the examples from the PEP use `*Ts` so I don't know if this is legal, but I hope so. This should probably be clarified in the PEP. -- Best regards, Willi Schinmeyer
I don't believe this is supported in pep 646 today. It was originally going to be supported with a Map operator. With a Map operator it would let you do something like, T = TypeVar('T') Ts = TypeVarTuple("Ts") IndexedTuple = Tuple[Int, T] def enumerage_args(*args: *Ts) -> *Map[IndexedTuple, Ts] return enumerate(args) Map operator takes two arguments, a generic type and type var tuple. This document describes map operator in more detail and an older version of the pep had it. https://docs.google.com/document/d/1szTVcFyLznoDT7phtT-6Fpvp27XaBw9DmbTLHrB6... The reason it is missing is original version of 646 was becoming too complex for a single pep. My understanding is your example/similar examples are intended for the future to be supported, but that Map operator and other extensions to variadic generics will be future peps.
Oops, sorry for the slow reply - I'm not subscribed to this mailing list. As Mehdi2277 says, this would indeed require the Map operator we'll introduce in a future PEP. But that's a good point about the `*Tuple[int, Ts]` syntax. I think the interpretation of it that would be most consistent with the rest of PEP 646 would actually be something slightly different than you had in mind - instead of saying that the Callable took args like Tuple[int, Ts[0]], Tuple[int, Ts[1]], ... it would say that the Callable took a variable number of arguments, the first of which was `int`, and the rest of which are bound to `Ts`. And this is indeed something we haven't talked about explicitly how to specify yet. Most of the discussion of PEP 646 has taken place on typing-sig, so I'll start a new thread there to discuss this.
participants (3)
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Matthew Rahtz -
Mehdi2277 -
willi＠schinmeyer.de