Arguments¶

A callable's parameter shape can be written as a type in its own right — see Anonymous class. The leftover arguments a signature doesn't name explicitly still need somewhere typed to go.

Call arguments already spread two ways: *expr distributes a sequence across positional slots, and **expr distributes a mapping across keyword arguments — the same two operations Positional arguments precede keyword arguments assumes throughout its examples.

Python collects a function's own leftover arguments the same way, but as two separate, untyped catch-alls: *args for the leftover positional values, **kwargs for the leftover keyword values, both essentially Any-typed for most of Python's history. Gather keeps that same split for the ordinary case — *name: T/**name: T, but checked against T, never Any.

The split form doesn't help a decorator or a proxy that needs to forward an unknown signature's entire overflow to another call, though: it still needs to carry *args and **kwargs as two separate, unrelated names everywhere they travel, exactly the case Python's own ParamSpec exists to type and still can't fully close (Decorators).

Lucid gathers leftover arguments meant for forwarding into one typed class instead:

class Arguments[Y, Z: ~dict[str, object]]:
    vpargs: list[Y]
    kwargs: Z

vpargs holds the leftover positional arguments, homogeneously typed; kwargs holds the leftover keyword arguments, typed as a full shape — dict[str, str], or a TypedDict shape when some of those keywords are individually named — bounded by ~dict[str, object] so that covariant read-only mappings satisfy it rather than invariant dict (see Mutability). Writing kwargs: str would say each value is a str, not that kwargs itself is a mapping; the field has to be annotated with what it actually holds.

Arguments on its own is for genuinely unnamed overflow: arguments beyond anything a function declared, with no name available to give them, and no fixed prefix left to keep separate. A signature with a fixed, named prefix to keep separate from that overflow needs Parameters instead, the class Arguments alone doesn't try to be.