Unpack

Type unpack operator.

The type unpack operator takes the child types from some container type,
such as `tuple[int, str]` or a `TypeVarTuple`, and 'pulls them out'.

For example::

    # For some generic class `Foo`:
    Foo[Unpack[tuple[int, str]]]  # Equivalent to Foo[int, str]

    Ts = TypeVarTuple('Ts')
    # Specifies that `Bar` is generic in an arbitrary number of types.
    # (Think of `Ts` as a tuple of an arbitrary number of individual
    #  `TypeVar`s, which the `Unpack` is 'pulling out' directly into the
    #  `Generic[]`.)
    class Bar(Generic[Unpack[Ts]]): ...
    Bar[int]  # Valid
    Bar[int, str]  # Also valid

From Python 3.11, this can also be done using the `*` operator::

    Foo[*tuple[int, str]]
    class Bar(Generic[*Ts]): ...

And from Python 3.12, it can be done using built-in syntax for generics::

    Foo[*tuple[int, str]]
    class Bar[*Ts]: ...

The operator can also be used along with a `TypedDict` to annotate
`**kwargs` in a function signature::

    class Movie(TypedDict):
        name: str
        year: int

    # This function expects two keyword arguments - *name* of type `str` and
    # *year* of type `int`.
    def foo(**kwargs: Unpack[Movie]): ...

Note that there is only some runtime checking of this operator. Not
everything the runtime allows is accepted by static type checkers.

For more information, see PEPs 646 and 692.