diff --git a/vm/src/builtins.rs b/vm/src/builtins.rs
index 7431ac439..78538e0fb 100644
--- a/vm/src/builtins.rs
+++ b/vm/src/builtins.rs
@@ -957,9 +957,8 @@ pub fn builtin_build_class_(
 
     function.invoke_with_scope(vec![].into(), &scope, vm)?;
 
-    let class = vm.call_method(
+    let class = vm.invoke(
         metaclass.as_object(),
-        "__call__",
         vec![name_obj, bases, namespace.into_object()],
     )?;
     cells.set_item("__class__", class.clone(), vm)?;
diff --git a/vm/src/lib.rs b/vm/src/lib.rs
index 444d87ccc..421984e90 100644
--- a/vm/src/lib.rs
+++ b/vm/src/lib.rs
@@ -59,7 +59,6 @@ pub mod macros;
 
 mod builtins;
 pub mod cformat;
-mod descriptor;
 mod dictdatatype;
 #[cfg(feature = "rustpython-compiler")]
 pub mod eval;
@@ -75,6 +74,7 @@ mod pyhash;
 pub mod pyobject;
 pub mod scope;
 mod sequence;
+mod slots;
 pub mod stdlib;
 mod sysmodule;
 pub mod types;
diff --git a/vm/src/macros.rs b/vm/src/macros.rs
index 7dca09f4d..4737d137a 100644
--- a/vm/src/macros.rs
+++ b/vm/src/macros.rs
@@ -169,7 +169,7 @@ macro_rules! py_namespace {
         {
             let namespace = $vm.ctx.new_namespace();
             $(
-                $vm.set_attr(&namespace, $name, $value).unwrap();
+                $vm.__module_set_attr(&namespace, $name, $value).unwrap();
             )*
             namespace
         }
diff --git a/vm/src/obj/objbuiltinfunc.rs b/vm/src/obj/objbuiltinfunc.rs
index 68780abd0..124eb4099 100644
--- a/vm/src/obj/objbuiltinfunc.rs
+++ b/vm/src/obj/objbuiltinfunc.rs
@@ -1,11 +1,11 @@
 use std::fmt;
 
-use crate::descriptor::PyBuiltinDescriptor;
 use crate::function::{OptionalArg, PyFuncArgs, PyNativeFunc};
 use crate::obj::objtype::PyClassRef;
 use crate::pyobject::{
     IdProtocol, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue, TypeProtocol,
 };
+use crate::slots::{PyBuiltinCallable, PyBuiltinDescriptor};
 use crate::vm::VirtualMachine;
 
 #[pyclass]
@@ -35,14 +35,15 @@ impl PyBuiltinFunction {
     }
 }
 
-#[pyimpl]
-impl PyBuiltinFunction {
-    #[pymethod(name = "__call__")]
-    pub fn call(&self, args: PyFuncArgs, vm: &VirtualMachine) -> PyResult {
+impl PyBuiltinCallable for PyBuiltinFunction {
+    fn call(&self, args: PyFuncArgs, vm: &VirtualMachine) -> PyResult {
         (self.value)(vm, args)
     }
 }
 
+#[pyimpl(with(PyBuiltinCallable))]
+impl PyBuiltinFunction {}
+
 #[pyclass]
 pub struct PyBuiltinMethod {
     function: PyBuiltinFunction,
@@ -87,14 +88,15 @@ impl PyBuiltinDescriptor for PyBuiltinMethod {
     }
 }
 
-#[pyimpl(with(PyBuiltinDescriptor))]
-impl PyBuiltinMethod {
-    #[pymethod(name = "__call__")]
-    pub fn call(&self, args: PyFuncArgs, vm: &VirtualMachine) -> PyResult {
-        self.function.call(args, vm)
+impl PyBuiltinCallable for PyBuiltinMethod {
+    fn call(&self, args: PyFuncArgs, vm: &VirtualMachine) -> PyResult {
+        (self.function.value)(vm, args)
     }
 }
 
+#[pyimpl(with(PyBuiltinDescriptor, PyBuiltinCallable))]
+impl PyBuiltinMethod {}
+
 pub fn init(context: &PyContext) {
     PyBuiltinFunction::extend_class(context, &context.types.builtin_function_or_method_type);
     PyBuiltinMethod::extend_class(context, &context.types.method_descriptor_type);
diff --git a/vm/src/obj/objclassmethod.rs b/vm/src/obj/objclassmethod.rs
index 2057c728d..34b652503 100644
--- a/vm/src/obj/objclassmethod.rs
+++ b/vm/src/obj/objclassmethod.rs
@@ -1,9 +1,9 @@
 use super::objtype::PyClassRef;
-use crate::descriptor::PyBuiltinDescriptor;
 use crate::function::OptionalArg;
 use crate::pyobject::{
     PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue, TypeProtocol,
 };
+use crate::slots::PyBuiltinDescriptor;
 use crate::vm::VirtualMachine;
 
 /// classmethod(function) -> method
diff --git a/vm/src/obj/objfunction.rs b/vm/src/obj/objfunction.rs
index ebeb004cd..f3b0e1fdb 100644
--- a/vm/src/obj/objfunction.rs
+++ b/vm/src/obj/objfunction.rs
@@ -4,7 +4,6 @@ use super::objstr::PyStringRef;
 use super::objtuple::PyTupleRef;
 use super::objtype::PyClassRef;
 use crate::bytecode;
-use crate::descriptor::PyBuiltinDescriptor;
 use crate::frame::Frame;
 use crate::function::{OptionalArg, PyFuncArgs};
 use crate::obj::objcoroutine::PyCoroutine;
@@ -14,6 +13,7 @@ use crate::pyobject::{
     TypeProtocol,
 };
 use crate::scope::Scope;
+use crate::slots::{PyBuiltinCallable, PyBuiltinDescriptor};
 use crate::vm::VirtualMachine;
 
 pub type PyFunctionRef = PyRef<PyFunction>;
@@ -242,9 +242,10 @@ impl PyValue for PyFunction {
 
 #[pyimpl(with(PyBuiltinDescriptor))]
 impl PyFunction {
+    #[pyslot]
     #[pymethod(magic)]
-    fn call(zelf: PyObjectRef, args: PyFuncArgs, vm: &VirtualMachine) -> PyResult {
-        vm.invoke(&zelf, args)
+    fn call(&self, args: PyFuncArgs, vm: &VirtualMachine) -> PyResult {
+        self.invoke(args, vm)
     }
 
     #[pyproperty(name = "__code__")]
@@ -263,6 +264,7 @@ impl PyFunction {
     }
 }
 
+#[pyclass]
 #[derive(Debug)]
 pub struct PyBoundMethod {
     // TODO: these shouldn't be public
@@ -270,11 +272,22 @@ pub struct PyBoundMethod {
     pub function: PyObjectRef,
 }
 
+impl PyBuiltinCallable for PyBoundMethod {
+    fn call(&self, args: PyFuncArgs, vm: &VirtualMachine) -> PyResult {
+        let args = args.insert(self.object.clone());
+        vm.invoke(&self.function, args)
+    }
+}
+
 impl PyBoundMethod {
     pub fn new(object: PyObjectRef, function: PyObjectRef) -> Self {
         PyBoundMethod { object, function }
     }
+}
 
+#[pyimpl(with(PyBuiltinCallable))]
+impl PyBoundMethod {
+    #[pymethod(magic)]
     fn getattribute(&self, name: PyStringRef, vm: &VirtualMachine) -> PyResult {
         vm.get_attribute(self.function.clone(), name)
     }
@@ -291,7 +304,5 @@ pub fn init(context: &PyContext) {
     PyFunction::extend_class(context, function_type);
 
     let method_type = &context.types.bound_method_type;
-    extend_class!(context, method_type, {
-        "__getattribute__" => context.new_method(PyBoundMethod::getattribute),
-    });
+    PyBoundMethod::extend_class(context, method_type);
 }
diff --git a/vm/src/obj/objobject.rs b/vm/src/obj/objobject.rs
index 0a1f1d554..e9aaa7622 100644
--- a/vm/src/obj/objobject.rs
+++ b/vm/src/obj/objobject.rs
@@ -77,7 +77,7 @@ fn object_hash(zelf: PyObjectRef, _vm: &VirtualMachine) -> pyhash::PyHash {
     zelf.get_id() as pyhash::PyHash
 }
 
-fn object_setattr(
+pub(crate) fn object_setattr(
     obj: PyObjectRef,
     attr_name: PyStringRef,
     value: PyObjectRef,
diff --git a/vm/src/obj/objproperty.rs b/vm/src/obj/objproperty.rs
index 8445243bf..26e53666b 100644
--- a/vm/src/obj/objproperty.rs
+++ b/vm/src/obj/objproperty.rs
@@ -4,12 +4,12 @@
 use std::cell::RefCell;
 
 use super::objtype::PyClassRef;
-use crate::descriptor::PyBuiltinDescriptor;
 use crate::function::{IntoPyNativeFunc, OptionalArg};
 use crate::pyobject::{
     IdProtocol, PyClassImpl, PyContext, PyObject, PyObjectRef, PyRef, PyResult, PyValue,
     TypeProtocol,
 };
+use crate::slots::PyBuiltinDescriptor;
 use crate::vm::VirtualMachine;
 
 // Read-only property, doesn't have __set__ or __delete__
diff --git a/vm/src/obj/objstaticmethod.rs b/vm/src/obj/objstaticmethod.rs
index 3cc2af92e..09c3608a6 100644
--- a/vm/src/obj/objstaticmethod.rs
+++ b/vm/src/obj/objstaticmethod.rs
@@ -1,7 +1,7 @@
 use super::objtype::PyClassRef;
-use crate::descriptor::PyBuiltinDescriptor;
 use crate::function::OptionalArg;
 use crate::pyobject::{PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue};
+use crate::slots::PyBuiltinDescriptor;
 use crate::vm::VirtualMachine;
 
 #[pyclass(name = "staticmethod")]
diff --git a/vm/src/obj/objtype.rs b/vm/src/obj/objtype.rs
index d5fe3e349..07625211c 100644
--- a/vm/src/obj/objtype.rs
+++ b/vm/src/obj/objtype.rs
@@ -9,11 +9,12 @@ use super::objproperty::PropertyBuilder;
 use super::objstr::PyStringRef;
 use super::objtuple::PyTuple;
 use super::objweakref::PyWeak;
-use crate::function::{PyFuncArgs, PyNativeFunc};
+use crate::function::PyFuncArgs;
 use crate::pyobject::{
     IdProtocol, PyAttributes, PyContext, PyIterable, PyObject, PyObjectRef, PyRef, PyResult,
     PyValue, TypeProtocol,
 };
+use crate::slots::PyClassSlots;
 use crate::vm::VirtualMachine;
 
 #[derive(Debug)]
@@ -26,18 +27,6 @@ pub struct PyClass {
     pub slots: RefCell<PyClassSlots>,
 }
 
-#[derive(Default)]
-pub struct PyClassSlots {
-    pub new: Option<PyNativeFunc>,
-    pub descr_get: Option<PyNativeFunc>,
-}
-
-impl fmt::Debug for PyClassSlots {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.write_str("PyClassSlots")
-    }
-}
-
 impl fmt::Display for PyClass {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Display::fmt(&self.name, f)
@@ -255,6 +244,7 @@ pub fn init(ctx: &PyContext) {
     extend_class!(&ctx, &ctx.types.type_type, {
         "mro" => ctx.new_method(type_mro),
         "__call__" => ctx.new_method(type_call),
+        (slot call) => type_call,
         "__dict__" =>
         PropertyBuilder::new(ctx)
                 .add_getter(type_dict)
diff --git a/vm/src/obj/objweakref.rs b/vm/src/obj/objweakref.rs
index e9ff727e8..f2764c012 100644
--- a/vm/src/obj/objweakref.rs
+++ b/vm/src/obj/objweakref.rs
@@ -1,12 +1,14 @@
 use super::objtype::PyClassRef;
-use crate::function::OptionalArg;
+use crate::function::{OptionalArg, PyFuncArgs};
 use crate::pyobject::{
-    PyContext, PyObject, PyObjectPayload, PyObjectRef, PyRef, PyResult, PyValue,
+    PyClassImpl, PyContext, PyObject, PyObjectPayload, PyObjectRef, PyRef, PyResult, PyValue,
 };
+use crate::slots::PyBuiltinCallable;
 use crate::vm::VirtualMachine;
 
 use std::rc::{Rc, Weak};
 
+#[pyclass]
 #[derive(Debug)]
 pub struct PyWeak {
     referent: Weak<PyObject<dyn PyObjectPayload>>,
@@ -32,25 +34,27 @@ impl PyValue for PyWeak {
 
 pub type PyWeakRef = PyRef<PyWeak>;
 
-impl PyWeakRef {
+impl PyBuiltinCallable for PyWeak {
+    fn call(&self, args: PyFuncArgs, vm: &VirtualMachine) -> PyResult {
+        args.bind::<()>(vm)?;
+        Ok(self.referent.upgrade().unwrap_or_else(|| vm.get_none()))
+    }
+}
+
+#[pyimpl(with(PyBuiltinCallable))]
+impl PyWeak {
     // TODO callbacks
-    fn create(
+    #[pyslot]
+    fn tp_new(
         cls: PyClassRef,
         referent: PyObjectRef,
         _callback: OptionalArg<PyObjectRef>,
         vm: &VirtualMachine,
-    ) -> PyResult<Self> {
+    ) -> PyResult<PyRef<Self>> {
         PyWeak::downgrade(&referent).into_ref_with_type(vm, cls)
     }
-
-    fn call(self, vm: &VirtualMachine) -> PyObjectRef {
-        self.referent.upgrade().unwrap_or_else(|| vm.get_none())
-    }
 }
 
 pub fn init(context: &PyContext) {
-    extend_class!(context, &context.types.weakref_type, {
-        (slot new) => PyWeakRef::create,
-        "__call__" => context.new_method(PyWeakRef::call)
-    });
+    PyWeak::extend_class(context, &context.types.weakref_type);
 }
diff --git a/vm/src/descriptor.rs b/vm/src/slots.rs
similarity index 50%
rename from vm/src/descriptor.rs
rename to vm/src/slots.rs
index f298224cf..ecb9660e5 100644
--- a/vm/src/descriptor.rs
+++ b/vm/src/slots.rs
@@ -1,10 +1,30 @@
-use crate::function::OptionalArg;
+use crate::function::{OptionalArg, PyFuncArgs, PyNativeFunc};
 use crate::pyobject::{IdProtocol, PyObjectRef, PyRef, PyResult, PyValue};
 use crate::VirtualMachine;
 
+#[derive(Default)]
+pub struct PyClassSlots {
+    pub new: Option<PyNativeFunc>,
+    pub call: Option<PyNativeFunc>,
+    pub descr_get: Option<PyNativeFunc>,
+}
+
+impl std::fmt::Debug for PyClassSlots {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("PyClassSlots")
+    }
+}
+
+#[pyimpl]
+pub trait PyBuiltinCallable: PyValue {
+    #[pymethod(magic)]
+    #[pyslot]
+    fn call(&self, args: PyFuncArgs, vm: &VirtualMachine) -> PyResult;
+}
+
 #[pyimpl]
 pub trait PyBuiltinDescriptor: PyValue {
-    #[pymethod(name = "__get__")]
+    #[pymethod(magic)]
     #[pyslot(descr_get)]
     fn get(
         zelf: PyRef<Self>,
diff --git a/vm/src/vm.rs b/vm/src/vm.rs
index 38762ca77..023c2473f 100644
--- a/vm/src/vm.rs
+++ b/vm/src/vm.rs
@@ -26,14 +26,13 @@ use crate::frozen;
 use crate::function::PyFuncArgs;
 use crate::import;
 use crate::obj::objbool;
-use crate::obj::objbuiltinfunc::{PyBuiltinFunction, PyBuiltinMethod};
 use crate::obj::objcode::{PyCode, PyCodeRef};
 use crate::obj::objdict::PyDictRef;
-use crate::obj::objfunction::{PyBoundMethod, PyFunction};
 use crate::obj::objint::PyInt;
 use crate::obj::objiter;
 use crate::obj::objlist::PyList;
 use crate::obj::objmodule::{self, PyModule};
+use crate::obj::objobject;
 use crate::obj::objstr::{PyString, PyStringRef};
 use crate::obj::objtuple::PyTuple;
 use crate::obj::objtype::{self, PyClassRef};
@@ -656,31 +655,23 @@ impl VirtualMachine {
         }
     }
 
-    fn _invoke(&self, func_ref: &PyObjectRef, args: PyFuncArgs) -> PyResult {
-        vm_trace!("Invoke: {:?} {:?}", func_ref, args);
-
-        if let Some(py_func) = func_ref.payload::<PyFunction>() {
+    fn _invoke(&self, callable: &PyObjectRef, args: PyFuncArgs) -> PyResult {
+        vm_trace!("Invoke: {:?} {:?}", callable, args);
+        let class = callable.class();
+        let slots = class.slots.borrow();
+        if let Some(slot_call) = slots.borrow().call.as_ref() {
             self.trace_event(TraceEvent::Call)?;
-            let res = py_func.invoke(args, self);
+            let args = args.insert(callable.clone());
+            let result = slot_call(self, args);
             self.trace_event(TraceEvent::Return)?;
-            res
-        } else if let Some(PyBoundMethod {
-            ref function,
-            ref object,
-        }) = func_ref.payload()
-        {
-            let args = args.insert(object.clone());
-            self.invoke(&function, args)
-        } else if let Some(builtin_func) = func_ref.payload::<PyBuiltinFunction>() {
-            builtin_func.as_func()(self, args)
-        } else if let Some(method) = func_ref.payload::<PyBuiltinMethod>() {
-            method.as_func()(self, args)
-        } else if self.is_callable(&func_ref) {
-            self.call_method(&func_ref, "__call__", args)
+            result
+        } else if objtype::class_has_attr(&class, "__call__") {
+            let result = self.call_method(&callable, "__call__", args);
+            result
         } else {
             Err(self.new_type_error(format!(
                 "'{}' object is not callable",
-                func_ref.class().name
+                callable.class().name
             )))
         }
     }
@@ -889,12 +880,8 @@ impl VirtualMachine {
     }
 
     pub fn is_callable(&self, obj: &PyObjectRef) -> bool {
-        match_class!(match obj {
-            PyFunction => true,
-            PyBoundMethod => true,
-            PyBuiltinFunction => true,
-            obj => objtype::class_has_attr(&obj.class(), "__call__"),
-        })
+        obj.class().slots.borrow().call.is_some()
+            || objtype::class_has_attr(&obj.class(), "__call__")
     }
 
     #[inline]
@@ -1311,8 +1298,7 @@ impl VirtualMachine {
         attr_value: impl Into<PyObjectRef>,
     ) -> PyResult<()> {
         let val = attr_value.into();
-        self.set_attr(module, attr_name, val)?;
-        Ok(())
+        objobject::object_setattr(module.clone(), attr_name.try_into_ref(self)?, val, self)
     }
 }