Method is_subclass

crates/vm/src/protocol/object.rs:534–575

Determines if `self` is a subclass of `cls`, either directly, indirectly or virtually via the __subclasscheck__ magic method. PyObject_IsSubclass/object_issubclass

(&self, cls: &Self, vm: &VirtualMachine)

    /// via the __subclasscheck__ magic method.
    /// PyObject_IsSubclass/object_issubclass
    pub fn is_subclass(&self, cls: &Self, vm: &VirtualMachine) -> PyResult<bool> {
        let derived = self;
        // PyType_CheckExact(cls)
        if cls.class().is(vm.ctx.types.type_type) {
            if derived.is(cls) {
                return Ok(true);
            }
            return derived.recursive_issubclass(cls, vm);
        }

        // Check for Union type - CPython handles this before tuple
        let cls = if cls.class().is(vm.ctx.types.union_type) {
            // Get the __args__ attribute which contains the union members
            // Match CPython's _Py_union_args which directly accesses the args field
            let union = cls
                .downcast_ref::<crate::builtins::PyUnion>()
                .expect("union is already checked");
            union.args().as_object()
        } else {
            cls
        };

        // Check if cls is a tuple
        if let Some(tuple) = cls.downcast_ref::<PyTuple>() {
            for item in tuple {
                if vm.with_recursion("in __subclasscheck__", || derived.is_subclass(item, vm))? {
                    return Ok(true);
                }
            }
            return Ok(false);
        }

        // Check for __subclasscheck__ method using lookup_special (matches CPython)
        if let Some(checker) = cls.lookup_special(identifier!(vm, __subclasscheck__), vm) {
            let res = vm.with_recursion("in __subclasscheck__", || {
                checker.call((derived.to_owned(),), vm)
            })?;
            return res.try_to_bool(vm);
        }

        derived.recursive_issubclass(cls, vm)
    }

    // _PyObject_RealIsInstance
    pub(crate) fn real_is_instance(&self, cls: &Self, vm: &VirtualMachine) -> PyResult<bool> {