diff --git a/vm/src/builtins/pytype.rs b/vm/src/builtins/pytype.rs
index 997419d14e..aeb407949f 100644
--- a/vm/src/builtins/pytype.rs
+++ b/vm/src/builtins/pytype.rs
@@ -1,6 +1,6 @@
 use super::{
-    mappingproxy::PyMappingProxy, object, PyClassMethod, PyDictRef, PyInt, PyList, PyStaticMethod,
-    PyStr, PyStrRef, PyTuple, PyTupleRef, PyWeak,
+    mappingproxy::PyMappingProxy, object, PyClassMethod, PyDictRef, PyList, PyStaticMethod, PyStr,
+    PyStrRef, PyTuple, PyTupleRef, PyWeak,
 };
 use crate::common::{
     ascii,
@@ -9,14 +9,11 @@ use crate::common::{
 };
 use crate::{
     function::{FuncArgs, KwArgs, OptionalArg},
-    protocol::{PyIterReturn, PyMappingMethods},
-    types::{self, Callable, PyComparisonOp, PyTypeFlags, PyTypeSlots, SlotGetattro, SlotSetattro},
-    utils::Either,
-    IdProtocol, PyAttributes, PyClassImpl, PyComparisonValue, PyContext, PyLease, PyObjectRef,
-    PyRef, PyResult, PyValue, StaticType, TypeProtocol, VirtualMachine,
+    types::{Callable, PyTypeFlags, PyTypeSlots, SlotGetattro, SlotSetattro},
+    IdProtocol, PyAttributes, PyClassImpl, PyContext, PyLease, PyObjectRef, PyRef, PyResult,
+    PyValue, StaticType, TypeProtocol, VirtualMachine,
 };
 use itertools::Itertools;
-use num_traits::ToPrimitive;
 use std::collections::HashSet;
 use std::fmt;
 use std::ops::Deref;
@@ -195,161 +192,6 @@ impl PyType {
 
         attributes
     }
-
-    pub(crate) fn update_slot(&self, name: &str, add: bool) {
-        macro_rules! update_slot {
-            ($name:ident, $func:expr) => {{
-                self.slots.$name.store(if add { Some($func) } else { None });
-            }};
-        }
-        match name {
-            "__new__" => {
-                let func: types::NewFunc =
-                    |cls: PyTypeRef, mut args: FuncArgs, vm: &VirtualMachine| {
-                        let new = vm
-                            .get_attribute_opt(cls.as_object().clone(), "__new__")?
-                            .unwrap();
-                        args.prepend_arg(cls.into());
-                        vm.invoke(&new, args)
-                    };
-                update_slot!(new, func);
-            }
-            "__call__" => {
-                let func: types::GenericMethod =
-                    |zelf, args, vm| vm.call_special_method(zelf.clone(), "__call__", args);
-                update_slot!(call, func);
-            }
-            "__get__" => {
-                let func: types::DescrGetFunc =
-                    |zelf, obj, cls, vm| vm.call_special_method(zelf, "__get__", (obj, cls));
-                update_slot!(descr_get, func);
-            }
-            "__set__" | "__delete__" => {
-                let func: types::DescrSetFunc = |zelf, obj, value, vm| {
-                    match value {
-                        Some(val) => vm.call_special_method(zelf, "__set__", (obj, val)),
-                        None => vm.call_special_method(zelf, "__delete__", (obj,)),
-                    }
-                    .map(drop)
-                };
-                update_slot!(descr_set, func);
-            }
-            "__hash__" => {
-                let func: types::HashFunc = |zelf, vm| {
-                    let hash_obj = vm.call_special_method(zelf.clone(), "__hash__", ())?;
-                    match hash_obj.payload_if_subclass::<PyInt>(vm) {
-                        Some(py_int) => {
-                            Ok(rustpython_common::hash::hash_bigint(py_int.as_bigint()))
-                        }
-                        None => Err(vm
-                            .new_type_error("__hash__ method should return an integer".to_owned())),
-                    }
-                } as _;
-                update_slot!(hash, func);
-            }
-            "__del__" => {
-                let func: types::DelFunc = |zelf, vm| {
-                    vm.call_special_method(zelf.clone(), "__del__", ())?;
-                    Ok(())
-                } as _;
-                update_slot!(del, func);
-            }
-            "__eq__" | "__ne__" | "__le__" | "__lt__" | "__ge__" | "__gt__" => {
-                update_slot!(richcompare, richcompare_wrapper);
-            }
-            "__getattribute__" => {
-                let func: types::GetattroFunc =
-                    |zelf, name, vm| vm.call_special_method(zelf, "__getattribute__", (name,));
-                update_slot!(getattro, func);
-            }
-            "__setattr__" => {
-                let func: types::SetattroFunc = |zelf, name, value, vm| {
-                    match value {
-                        Some(value) => {
-                            vm.call_special_method(zelf.clone(), "__setattr__", (name, value))?;
-                        }
-                        None => {
-                            vm.call_special_method(zelf.clone(), "__delattr__", (name,))?;
-                        }
-                    };
-                    Ok(())
-                };
-                update_slot!(setattro, func);
-            }
-            "__iter__" => {
-                let func: types::IterFunc = |zelf, vm| vm.call_special_method(zelf, "__iter__", ());
-                update_slot!(iter, func);
-            }
-            "__next__" => {
-                let func: types::IterNextFunc = |zelf, vm| {
-                    PyIterReturn::from_pyresult(
-                        vm.call_special_method(zelf.clone(), "__next__", ()),
-                        vm,
-                    )
-                };
-                update_slot!(iternext, func);
-            }
-            "__len__" | "__getitem__" | "__setitem__" | "__delitem__" => {
-                macro_rules! then_some_closure {
-                    ($cond:expr, $closure:expr) => {
-                        if $cond {
-                            Some($closure)
-                        } else {
-                            None
-                        }
-                    };
-                }
-
-                let func: types::MappingFunc = |zelf, _vm| {
-                    Ok(PyMappingMethods {
-                        length: then_some_closure!(zelf.has_class_attr("__len__"), |zelf, vm| {
-                            vm.call_special_method(zelf, "__len__", ()).map(|obj| {
-                                obj.payload_if_subclass::<PyInt>(vm)
-                                    .map(|length_obj| {
-                                        length_obj.as_bigint().to_usize().ok_or_else(|| {
-                                            vm.new_value_error(
-                                                "__len__() should return >= 0".to_owned(),
-                                            )
-                                        })
-                                    })
-                                    .unwrap()
-                            })?
-                        }),
-                        subscript: then_some_closure!(
-                            zelf.has_class_attr("__getitem__"),
-                            |zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine| {
-                                vm.call_special_method(zelf, "__getitem__", (needle,))
-                            }
-                        ),
-                        ass_subscript: then_some_closure!(
-                            zelf.has_class_attr("__setitem__") | zelf.has_class_attr("__delitem__"),
-                            |zelf, needle, value, vm| match value {
-                                Some(value) => vm
-                                    .call_special_method(zelf, "__setitem__", (needle, value),)
-                                    .map(|_| Ok(()))?,
-                                None => vm
-                                    .call_special_method(zelf, "__delitem__", (needle,))
-                                    .map(|_| Ok(()))?,
-                            }
-                        ),
-                    })
-                };
-                update_slot!(as_mapping, func);
-                // TODO: need to update sequence protocol too
-            }
-            _ => {}
-        }
-    }
-}
-
-fn richcompare_wrapper(
-    zelf: &PyObjectRef,
-    other: &PyObjectRef,
-    op: PyComparisonOp,
-    vm: &VirtualMachine,
-) -> PyResult<Either<PyObjectRef, PyComparisonValue>> {
-    vm.call_special_method(zelf.clone(), op.method_name(), (other.clone(),))
-        .map(Either::A)
 }
 
 impl PyTypeRef {
diff --git a/vm/src/types/slot.rs b/vm/src/types/slot.rs
index 10a64cc00b..146fda3c09 100644
--- a/vm/src/types/slot.rs
+++ b/vm/src/types/slot.rs
@@ -1,6 +1,6 @@
 use crate::common::{hash::PyHash, lock::PyRwLock};
 use crate::{
-    builtins::{PyStrRef, PyTypeRef},
+    builtins::{PyInt, PyStrRef, PyType, PyTypeRef},
     function::{FromArgs, FuncArgs, IntoPyResult, OptionalArg},
     protocol::{PyBuffer, PyIterReturn, PyMappingMethods},
     utils::Either,
@@ -8,70 +8,9 @@ use crate::{
     VirtualMachine,
 };
 use crossbeam_utils::atomic::AtomicCell;
+use num_traits::ToPrimitive;
 use std::cmp::Ordering;
 
-bitflags! {
-    pub struct PyTypeFlags: u64 {
-        const HEAPTYPE = 1 << 9;
-        const BASETYPE = 1 << 10;
-        const METHOD_DESCR = 1 << 17;
-        const HAS_DICT = 1 << 40;
-
-        #[cfg(debug_assertions)]
-        const _CREATED_WITH_FLAGS = 1 << 63;
-    }
-}
-
-impl PyTypeFlags {
-    // Default used for both built-in and normal classes: empty, for now.
-    // CPython default: Py_TPFLAGS_HAVE_STACKLESS_EXTENSION | Py_TPFLAGS_HAVE_VERSION_TAG
-    pub const DEFAULT: Self = Self::empty();
-
-    // CPython: See initialization of flags in type_new.
-    /// Used for types created in Python. Subclassable and are a
-    /// heaptype.
-    pub fn heap_type_flags() -> Self {
-        Self::DEFAULT | Self::HEAPTYPE | Self::BASETYPE
-    }
-
-    pub fn has_feature(self, flag: Self) -> bool {
-        self.contains(flag)
-    }
-
-    #[cfg(debug_assertions)]
-    pub fn is_created_with_flags(self) -> bool {
-        self.contains(Self::_CREATED_WITH_FLAGS)
-    }
-}
-
-impl Default for PyTypeFlags {
-    fn default() -> Self {
-        Self::DEFAULT
-    }
-}
-
-pub(crate) type GenericMethod = fn(&PyObjectRef, FuncArgs, &VirtualMachine) -> PyResult;
-pub(crate) type NewFunc = fn(PyTypeRef, FuncArgs, &VirtualMachine) -> PyResult;
-pub(crate) type DelFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<()>;
-pub(crate) type DescrGetFunc =
-    fn(PyObjectRef, Option<PyObjectRef>, Option<PyObjectRef>, &VirtualMachine) -> PyResult;
-pub(crate) type DescrSetFunc =
-    fn(PyObjectRef, PyObjectRef, Option<PyObjectRef>, &VirtualMachine) -> PyResult<()>;
-pub(crate) type HashFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyHash>;
-pub(crate) type RichCompareFunc = fn(
-    &PyObjectRef,
-    &PyObjectRef,
-    PyComparisonOp,
-    &VirtualMachine,
-) -> PyResult<Either<PyObjectRef, PyComparisonValue>>;
-pub(crate) type GetattroFunc = fn(PyObjectRef, PyStrRef, &VirtualMachine) -> PyResult;
-pub(crate) type SetattroFunc =
-    fn(&PyObjectRef, PyStrRef, Option<PyObjectRef>, &VirtualMachine) -> PyResult<()>;
-pub(crate) type BufferFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyBuffer>;
-pub(crate) type MappingFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyMappingMethods>;
-pub(crate) type IterFunc = fn(PyObjectRef, &VirtualMachine) -> PyResult;
-pub(crate) type IterNextFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyIterReturn>;
-
 // The corresponding field in CPython is `tp_` prefixed.
 // e.g. name -> tp_name
 #[derive(Default)]
@@ -84,7 +23,7 @@ pub struct PyTypeSlots {
     // Method suites for standard classes
     // tp_as_number
     // tp_as_sequence
-    pub as_mapping: AtomicCell<Option<MappingFunc>>,
+    pub as_mapping: AtomicCell<Option<AsMappingFunc>>,
 
     // More standard operations (here for binary compatibility)
     pub hash: AtomicCell<Option<HashFunc>>,
@@ -94,7 +33,7 @@ pub struct PyTypeSlots {
     pub setattro: AtomicCell<Option<SetattroFunc>>,
 
     // Functions to access object as input/output buffer
-    pub as_buffer: Option<BufferFunc>,
+    pub as_buffer: Option<AsBufferFunc>,
 
     // Assigned meaning in release 2.1
     // rich comparisons
@@ -144,6 +83,250 @@ impl std::fmt::Debug for PyTypeSlots {
     }
 }
 
+bitflags! {
+    pub struct PyTypeFlags: u64 {
+        const HEAPTYPE = 1 << 9;
+        const BASETYPE = 1 << 10;
+        const METHOD_DESCR = 1 << 17;
+        const HAS_DICT = 1 << 40;
+
+        #[cfg(debug_assertions)]
+        const _CREATED_WITH_FLAGS = 1 << 63;
+    }
+}
+
+impl PyTypeFlags {
+    // Default used for both built-in and normal classes: empty, for now.
+    // CPython default: Py_TPFLAGS_HAVE_STACKLESS_EXTENSION | Py_TPFLAGS_HAVE_VERSION_TAG
+    pub const DEFAULT: Self = Self::empty();
+
+    // CPython: See initialization of flags in type_new.
+    /// Used for types created in Python. Subclassable and are a
+    /// heaptype.
+    pub fn heap_type_flags() -> Self {
+        Self::DEFAULT | Self::HEAPTYPE | Self::BASETYPE
+    }
+
+    pub fn has_feature(self, flag: Self) -> bool {
+        self.contains(flag)
+    }
+
+    #[cfg(debug_assertions)]
+    pub fn is_created_with_flags(self) -> bool {
+        self.contains(Self::_CREATED_WITH_FLAGS)
+    }
+}
+
+impl Default for PyTypeFlags {
+    fn default() -> Self {
+        Self::DEFAULT
+    }
+}
+
+pub(crate) type GenericMethod = fn(&PyObjectRef, FuncArgs, &VirtualMachine) -> PyResult;
+pub(crate) type AsMappingFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyMappingMethods>;
+pub(crate) type HashFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyHash>;
+// CallFunc = GenericMethod
+pub(crate) type GetattroFunc = fn(PyObjectRef, PyStrRef, &VirtualMachine) -> PyResult;
+pub(crate) type SetattroFunc =
+    fn(&PyObjectRef, PyStrRef, Option<PyObjectRef>, &VirtualMachine) -> PyResult<()>;
+pub(crate) type AsBufferFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyBuffer>;
+pub(crate) type RichCompareFunc = fn(
+    &PyObjectRef,
+    &PyObjectRef,
+    PyComparisonOp,
+    &VirtualMachine,
+) -> PyResult<Either<PyObjectRef, PyComparisonValue>>;
+pub(crate) type IterFunc = fn(PyObjectRef, &VirtualMachine) -> PyResult;
+pub(crate) type IterNextFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyIterReturn>;
+pub(crate) type DescrGetFunc =
+    fn(PyObjectRef, Option<PyObjectRef>, Option<PyObjectRef>, &VirtualMachine) -> PyResult;
+pub(crate) type DescrSetFunc =
+    fn(PyObjectRef, PyObjectRef, Option<PyObjectRef>, &VirtualMachine) -> PyResult<()>;
+pub(crate) type NewFunc = fn(PyTypeRef, FuncArgs, &VirtualMachine) -> PyResult;
+pub(crate) type DelFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<()>;
+
+fn as_mapping_wrapper(zelf: &PyObjectRef, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+    macro_rules! then_some_closure {
+        ($cond:expr, $closure:expr) => {
+            if $cond {
+                Some($closure)
+            } else {
+                None
+            }
+        };
+    }
+    Ok(PyMappingMethods {
+        length: then_some_closure!(zelf.has_class_attr("__len__"), |zelf, vm| {
+            vm.call_special_method(zelf, "__len__", ()).map(|obj| {
+                obj.payload_if_subclass::<PyInt>(vm)
+                    .map(|length_obj| {
+                        length_obj.as_bigint().to_usize().ok_or_else(|| {
+                            vm.new_value_error("__len__() should return >= 0".to_owned())
+                        })
+                    })
+                    .unwrap()
+            })?
+        }),
+        subscript: then_some_closure!(
+            zelf.has_class_attr("__getitem__"),
+            |zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine| {
+                vm.call_special_method(zelf, "__getitem__", (needle,))
+            }
+        ),
+        ass_subscript: then_some_closure!(
+            zelf.has_class_attr("__setitem__") | zelf.has_class_attr("__delitem__"),
+            |zelf, needle, value, vm| match value {
+                Some(value) => vm
+                    .call_special_method(zelf, "__setitem__", (needle, value),)
+                    .map(|_| Ok(()))?,
+                None => vm
+                    .call_special_method(zelf, "__delitem__", (needle,))
+                    .map(|_| Ok(()))?,
+            }
+        ),
+    })
+}
+
+fn hash_wrapper(zelf: &PyObjectRef, vm: &VirtualMachine) -> PyResult<PyHash> {
+    let hash_obj = vm.call_special_method(zelf.clone(), "__hash__", ())?;
+    match hash_obj.payload_if_subclass::<PyInt>(vm) {
+        Some(py_int) => Ok(rustpython_common::hash::hash_bigint(py_int.as_bigint())),
+        None => Err(vm.new_type_error("__hash__ method should return an integer".to_owned())),
+    }
+}
+
+fn call_wrapper(zelf: &PyObjectRef, args: FuncArgs, vm: &VirtualMachine) -> PyResult {
+    vm.call_special_method(zelf.clone(), "__call__", args)
+}
+
+fn getattro_wrapper(zelf: PyObjectRef, name: PyStrRef, vm: &VirtualMachine) -> PyResult {
+    vm.call_special_method(zelf, "__getattribute__", (name,))
+}
+
+fn setattro_wrapper(
+    zelf: &PyObjectRef,
+    name: PyStrRef,
+    value: Option<PyObjectRef>,
+    vm: &VirtualMachine,
+) -> PyResult<()> {
+    match value {
+        Some(value) => {
+            vm.call_special_method(zelf.clone(), "__setattr__", (name, value))?;
+        }
+        None => {
+            vm.call_special_method(zelf.clone(), "__delattr__", (name,))?;
+        }
+    };
+    Ok(())
+}
+
+fn richcompare_wrapper(
+    zelf: &PyObjectRef,
+    other: &PyObjectRef,
+    op: PyComparisonOp,
+    vm: &VirtualMachine,
+) -> PyResult<Either<PyObjectRef, PyComparisonValue>> {
+    vm.call_special_method(zelf.clone(), op.method_name(), (other.clone(),))
+        .map(Either::A)
+}
+
+fn iter_wrapper(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+    vm.call_special_method(zelf, "__iter__", ())
+}
+
+fn iternext_wrapper(zelf: &PyObjectRef, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+    PyIterReturn::from_pyresult(vm.call_special_method(zelf.clone(), "__next__", ()), vm)
+}
+
+fn descr_get_wrapper(
+    zelf: PyObjectRef,
+    obj: Option<PyObjectRef>,
+    cls: Option<PyObjectRef>,
+    vm: &VirtualMachine,
+) -> PyResult {
+    vm.call_special_method(zelf, "__get__", (obj, cls))
+}
+
+fn descr_set_wrapper(
+    zelf: PyObjectRef,
+    obj: PyObjectRef,
+    value: Option<PyObjectRef>,
+    vm: &VirtualMachine,
+) -> PyResult<()> {
+    match value {
+        Some(val) => vm.call_special_method(zelf, "__set__", (obj, val)),
+        None => vm.call_special_method(zelf, "__delete__", (obj,)),
+    }
+    .map(drop)
+}
+
+fn new_wrapper(cls: PyTypeRef, mut args: FuncArgs, vm: &VirtualMachine) -> PyResult {
+    let new = vm
+        .get_attribute_opt(cls.as_object().clone(), "__new__")?
+        .unwrap();
+    args.prepend_arg(cls.into());
+    vm.invoke(&new, args)
+}
+
+fn del_wrapper(zelf: &PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
+    vm.call_special_method(zelf.clone(), "__del__", ())?;
+    Ok(())
+}
+
+impl PyType {
+    pub(crate) fn update_slot(&self, name: &str, add: bool) {
+        debug_assert!(name.starts_with("__"));
+        debug_assert!(name.ends_with("__"));
+
+        macro_rules! update_slot {
+            ($name:ident, $func:expr) => {{
+                self.slots.$name.store(if add { Some($func) } else { None });
+            }};
+        }
+        match name {
+            "__len__" | "__getitem__" | "__setitem__" | "__delitem__" => {
+                update_slot!(as_mapping, as_mapping_wrapper);
+                // TODO: need to update sequence protocol too
+            }
+            "__hash__" => {
+                update_slot!(hash, hash_wrapper);
+            }
+            "__call__" => {
+                update_slot!(call, call_wrapper);
+            }
+            "__getattribute__" => {
+                update_slot!(getattro, getattro_wrapper);
+            }
+            "__setattr__" | "__delattr__" => {
+                update_slot!(setattro, setattro_wrapper);
+            }
+            "__eq__" | "__ne__" | "__le__" | "__lt__" | "__ge__" | "__gt__" => {
+                update_slot!(richcompare, richcompare_wrapper);
+            }
+            "__iter__" => {
+                update_slot!(iter, iter_wrapper);
+            }
+            "__next__" => {
+                update_slot!(iternext, iternext_wrapper);
+            }
+            "__get__" => {
+                update_slot!(descr_get, descr_get_wrapper);
+            }
+            "__set__" | "__delete__" => {
+                update_slot!(descr_set, descr_set_wrapper);
+            }
+            "__new__" => {
+                update_slot!(new, new_wrapper);
+            }
+            "__del__" => {
+                update_slot!(del, del_wrapper);
+            }
+            _ => {}
+        }
+    }
+}
+
 #[pyimpl]
 pub trait SlotConstructor: PyValue {
     type Args: FromArgs;