Class _TypedDictMeta

Lib/typing.py:3174–3311

class _TypedDictMeta(type):
    def __new__(cls, name, bases, ns, total=True, closed=None,
                extra_items=NoExtraItems):
        """Create a new typed dict class object.

        This method is called when TypedDict is subclassed,
        or when TypedDict is instantiated. This way
        TypedDict supports all three syntax forms described in its docstring.
        Subclasses and instances of TypedDict return actual dictionaries.
        """
        for base in bases:
            if type(base) is not _TypedDictMeta and base is not Generic:
                raise TypeError('cannot inherit from both a TypedDict type '
                                'and a non-TypedDict base class')
        if closed is not None and extra_items is not NoExtraItems:
            raise TypeError(f"Cannot combine closed={closed!r} and extra_items")

        if any(issubclass(b, Generic) for b in bases):
            generic_base = (Generic,)
        else:
            generic_base = ()

        ns_annotations = ns.pop('__annotations__', None)

        tp_dict = type.__new__(_TypedDictMeta, name, (*generic_base, dict), ns)

        if not hasattr(tp_dict, '__orig_bases__'):
            tp_dict.__orig_bases__ = bases

        if ns_annotations is not None:
            own_annotate = None
            own_annotations = ns_annotations
        elif (own_annotate := _lazy_annotationlib.get_annotate_from_class_namespace(ns)) is not None:
            own_annotations = _lazy_annotationlib.call_annotate_function(
                own_annotate, _lazy_annotationlib.Format.FORWARDREF, owner=tp_dict
            )
        else:
            own_annotate = None
            own_annotations = {}
        msg = "TypedDict('Name', {f0: t0, f1: t1, ...}); each t must be a type"
        own_checked_annotations = {
            n: _type_check(tp, msg, owner=tp_dict, module=tp_dict.__module__)
            for n, tp in own_annotations.items()
        }
        required_keys = set()
        optional_keys = set()
        readonly_keys = set()
        mutable_keys = set()

        for base in bases:
            base_required = base.__dict__.get('__required_keys__', set())
            required_keys |= base_required
            optional_keys -= base_required

            base_optional = base.__dict__.get('__optional_keys__', set())
            required_keys -= base_optional
            optional_keys |= base_optional