Generic builtins

Unbound inherited methods

In typeshed, list inherits clear from MutableSequence, and dict inherits it from MutableMapping. We can call these methods through list and dict without supplying type arguments.

def clear_containers(items: list[int], mapping: dict[str, int]) -> None:
    list.clear(items)
    dict.clear(mapping)

Variadic keyword arguments with a custom dict

When we define dict in a custom typeshed, we must take care to define it as a generic class in the same way as in the real typeshed.

[environment]
typeshed = "/typeshed"

/typeshed/stdlib/builtins.pyi:

class object: ...
class int: ...
class tuple: ...
class dict[K, V, Extra]: ...

/typeshed/stdlib/typing_extensions.pyi:

def reveal_type(obj, /): ...

If we don't, then we may get "surprising" results when inferring the types of variadic keyword arguments.

def f(**kwargs):
    reveal_type(kwargs)  # revealed: dict[Unknown, Unknown, Unknown]

def g(**kwargs: int):
    reveal_type(kwargs)  # revealed: dict[Unknown, Unknown, Unknown]