diff --git a/stdlib/src/array.rs b/stdlib/src/array.rs
index 29a675e110..77273bda90 100644
--- a/stdlib/src/array.rs
+++ b/stdlib/src/array.rs
@@ -17,11 +17,13 @@ mod array {
         },
         class_or_notimplemented,
         function::{ArgBytesLike, ArgIterable, OptionalArg},
-        protocol::{BufferInternal, BufferOptions, PyBuffer, PyIterReturn, ResizeGuard},
+        protocol::{
+            BufferInternal, BufferOptions, PyBuffer, PyIterReturn, PyMappingMethods, ResizeGuard,
+        },
         sliceable::{saturate_index, PySliceableSequence, PySliceableSequenceMut, SequenceIndex},
         slots::{
-            AsBuffer, Comparable, Iterable, IteratorIterable, PyComparisonOp, SlotConstructor,
-            SlotIterator,
+            AsBuffer, AsMapping, Comparable, Iterable, IteratorIterable, PyComparisonOp,
+            SlotConstructor, SlotIterator,
         },
         IdProtocol, IntoPyObject, IntoPyResult, PyComparisonValue, PyObjectRef, PyRef, PyResult,
         PyValue, TryFromObject, TypeProtocol, VirtualMachine,
@@ -665,7 +667,10 @@ mod array {
         }
     }
 
-    #[pyimpl(flags(BASETYPE), with(Comparable, AsBuffer, Iterable, SlotConstructor))]
+    #[pyimpl(
+        flags(BASETYPE),
+        with(Comparable, AsBuffer, AsMapping, Iterable, SlotConstructor)
+    )]
     impl PyArray {
         fn read(&self) -> PyRwLockReadGuard<'_, ArrayContentType> {
             self.array.read()
@@ -1161,6 +1166,38 @@ mod array {
         }
     }
 
+    impl AsMapping for PyArray {
+        fn as_mapping(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+            Ok(PyMappingMethods {
+                length: Some(Self::length),
+                subscript: Some(Self::subscript),
+                ass_subscript: Some(Self::ass_subscript),
+            })
+        }
+
+        fn length(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+            Self::downcast_ref(&zelf, vm).map(|zelf| Ok(zelf.len()))?
+        }
+
+        fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+            Self::downcast_ref(&zelf, vm).map(|zelf| zelf.getitem(needle, vm))?
+        }
+
+        fn ass_subscript(
+            zelf: PyObjectRef,
+            needle: PyObjectRef,
+            value: Option<PyObjectRef>,
+            vm: &VirtualMachine,
+        ) -> PyResult<()> {
+            match value {
+                Some(value) => {
+                    Self::downcast(zelf, vm).map(|zelf| Self::setitem(zelf, needle, value, vm))?
+                }
+                None => Self::downcast(zelf, vm).map(|zelf| Self::delitem(zelf, needle, vm))?,
+            }
+        }
+    }
+
     impl Iterable for PyArray {
         fn iter(zelf: PyRef<Self>, vm: &VirtualMachine) -> PyResult {
             Ok(PyArrayIter {
diff --git a/vm/src/builtins/bytearray.rs b/vm/src/builtins/bytearray.rs
index 2ab6091dcd..2d8e4c849f 100644
--- a/vm/src/builtins/bytearray.rs
+++ b/vm/src/builtins/bytearray.rs
@@ -15,11 +15,13 @@ use crate::{
         ByteInnerTranslateOptions, DecodeArgs, PyBytesInner,
     },
     function::{ArgBytesLike, ArgIterable, FuncArgs, OptionalArg, OptionalOption},
-    protocol::{BufferInternal, BufferOptions, PyBuffer, PyIterReturn, ResizeGuard},
+    protocol::{
+        BufferInternal, BufferOptions, PyBuffer, PyIterReturn, PyMappingMethods, ResizeGuard,
+    },
     sliceable::{PySliceableSequence, PySliceableSequenceMut, SequenceIndex},
     slots::{
-        AsBuffer, Callable, Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp,
-        SlotIterator, Unhashable,
+        AsBuffer, AsMapping, Callable, Comparable, Hashable, Iterable, IteratorIterable,
+        PyComparisonOp, SlotIterator, Unhashable,
     },
     utils::Either,
     IdProtocol, IntoPyObject, PyClassDef, PyClassImpl, PyComparisonValue, PyContext, PyObjectRef,
@@ -95,7 +97,10 @@ pub(crate) fn init(context: &PyContext) {
     PyByteArrayIterator::extend_class(context, &context.types.bytearray_iterator_type);
 }
 
-#[pyimpl(flags(BASETYPE), with(Hashable, Comparable, AsBuffer, Iterable))]
+#[pyimpl(
+    flags(BASETYPE),
+    with(Hashable, Comparable, AsBuffer, AsMapping, Iterable)
+)]
 impl PyByteArray {
     #[pyslot]
     fn slot_new(cls: PyTypeRef, _args: FuncArgs, vm: &VirtualMachine) -> PyResult {
@@ -201,9 +206,9 @@ impl PyByteArray {
     }
 
     #[pymethod(magic)]
-    pub fn delitem(&self, needle: SequenceIndex, vm: &VirtualMachine) -> PyResult<()> {
+    pub fn delitem(&self, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
         let elements = &mut self.try_resizable(vm)?.elements;
-        match needle {
+        match SequenceIndex::try_from_object_for(vm, needle, Self::NAME)? {
             SequenceIndex::Int(int) => {
                 if let Some(idx) = elements.wrap_index(int) {
                     elements.remove(idx);
@@ -712,6 +717,41 @@ impl<'a> ResizeGuard<'a> for PyByteArray {
     }
 }
 
+impl AsMapping for PyByteArray {
+    fn as_mapping(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+        Ok(PyMappingMethods {
+            length: Some(Self::length),
+            subscript: Some(Self::subscript),
+            ass_subscript: Some(Self::ass_subscript),
+        })
+    }
+
+    #[inline]
+    fn length(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+        Self::downcast_ref(&zelf, vm).map(|zelf| Ok(zelf.len()))?
+    }
+
+    #[inline]
+    fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        Self::downcast_ref(&zelf, vm).map(|zelf| zelf.getitem(needle, vm))?
+    }
+
+    #[inline]
+    fn ass_subscript(
+        zelf: PyObjectRef,
+        needle: PyObjectRef,
+        value: Option<PyObjectRef>,
+        vm: &VirtualMachine,
+    ) -> PyResult<()> {
+        match value {
+            Some(value) => {
+                Self::downcast(zelf, vm).map(|zelf| Self::setitem(zelf, needle, value, vm))
+            }
+            None => Self::downcast_ref(&zelf, vm).map(|zelf| zelf.delitem(needle, vm)),
+        }?
+    }
+}
+
 impl Unhashable for PyByteArray {}
 
 impl Iterable for PyByteArray {
diff --git a/vm/src/builtins/bytes.rs b/vm/src/builtins/bytes.rs
index 2df6000179..f24d5e345e 100644
--- a/vm/src/builtins/bytes.rs
+++ b/vm/src/builtins/bytes.rs
@@ -7,10 +7,10 @@ use crate::{
     },
     common::hash::PyHash,
     function::{ArgBytesLike, ArgIterable, OptionalArg, OptionalOption},
-    protocol::{BufferInternal, BufferOptions, PyBuffer, PyIterReturn},
+    protocol::{BufferInternal, BufferOptions, PyBuffer, PyIterReturn, PyMappingMethods},
     slots::{
-        AsBuffer, Callable, Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp,
-        SlotConstructor, SlotIterator,
+        AsBuffer, AsMapping, Callable, Comparable, Hashable, Iterable, IteratorIterable,
+        PyComparisonOp, SlotConstructor, SlotIterator,
     },
     utils::Either,
     IdProtocol, IntoPyObject, IntoPyResult, PyClassImpl, PyComparisonValue, PyContext, PyObjectRef,
@@ -103,7 +103,7 @@ impl SlotConstructor for PyBytes {
 
 #[pyimpl(
     flags(BASETYPE),
-    with(Hashable, Comparable, AsBuffer, Iterable, SlotConstructor)
+    with(AsMapping, Hashable, Comparable, AsBuffer, Iterable, SlotConstructor)
 )]
 impl PyBytes {
     #[pymethod(magic)]
@@ -540,6 +540,36 @@ impl BufferInternal for PyRef<PyBytes> {
     fn retain(&self) {}
 }
 
+impl AsMapping for PyBytes {
+    fn as_mapping(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+        Ok(PyMappingMethods {
+            length: Some(Self::length),
+            subscript: Some(Self::subscript),
+            ass_subscript: None,
+        })
+    }
+
+    #[inline]
+    fn length(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+        Self::downcast_ref(&zelf, vm).map(|zelf| Ok(zelf.len()))?
+    }
+
+    #[inline]
+    fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        Self::downcast_ref(&zelf, vm).map(|zelf| zelf.getitem(needle, vm))?
+    }
+
+    #[cold]
+    fn ass_subscript(
+        zelf: PyObjectRef,
+        _needle: PyObjectRef,
+        _value: Option<PyObjectRef>,
+        _vm: &VirtualMachine,
+    ) -> PyResult<()> {
+        unreachable!("ass_subscript not implemented for {}", zelf.class())
+    }
+}
+
 impl Hashable for PyBytes {
     fn hash(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyHash> {
         Ok(zelf.inner.hash(vm))
diff --git a/vm/src/builtins/dict.rs b/vm/src/builtins/dict.rs
index c35b100c76..122831d0b4 100644
--- a/vm/src/builtins/dict.rs
+++ b/vm/src/builtins/dict.rs
@@ -4,15 +4,16 @@ use crate::{
     common::ascii,
     dictdatatype::{self, DictKey},
     function::{ArgIterable, FuncArgs, KwArgs, OptionalArg},
-    protocol::PyIterReturn,
+    protocol::{PyIterReturn, PyMappingMethods},
     slots::{
-        Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotIterator, Unhashable,
+        AsMapping, Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotIterator,
+        Unhashable,
     },
     vm::{ReprGuard, VirtualMachine},
     IdProtocol, IntoPyObject, ItemProtocol,
     PyArithmeticValue::*,
     PyAttributes, PyClassDef, PyClassImpl, PyComparisonValue, PyContext, PyObjectRef, PyRef,
-    PyResult, PyValue, TryFromObject, TypeProtocol,
+    PyResult, PyValue, TypeProtocol,
 };
 use crossbeam_utils::atomic::AtomicCell;
 use std::fmt;
@@ -51,7 +52,7 @@ impl PyValue for PyDict {
 
 // Python dict methods:
 #[allow(clippy::len_without_is_empty)]
-#[pyimpl(with(Hashable, Comparable, Iterable), flags(BASETYPE))]
+#[pyimpl(with(AsMapping, Hashable, Comparable, Iterable), flags(BASETYPE))]
 impl PyDict {
     #[pyslot]
     fn slot_new(cls: PyTypeRef, _args: FuncArgs, vm: &VirtualMachine) -> PyResult {
@@ -410,6 +411,39 @@ impl PyDict {
     }
 }
 
+impl AsMapping for PyDict {
+    fn as_mapping(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+        Ok(PyMappingMethods {
+            length: Some(Self::length),
+            subscript: Some(Self::subscript),
+            ass_subscript: Some(Self::ass_subscript),
+        })
+    }
+
+    #[inline]
+    fn length(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+        Self::downcast_ref(&zelf, vm).map(|zelf| Ok(zelf.len()))?
+    }
+
+    #[inline]
+    fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        Self::downcast(zelf, vm).map(|zelf| Self::getitem(zelf, needle, vm))?
+    }
+
+    #[inline]
+    fn ass_subscript(
+        zelf: PyObjectRef,
+        needle: PyObjectRef,
+        value: Option<PyObjectRef>,
+        vm: &VirtualMachine,
+    ) -> PyResult<()> {
+        Self::downcast_ref(&zelf, vm).map(|zelf| match value {
+            Some(value) => zelf.setitem(needle, value, vm),
+            None => zelf.delitem(needle, vm),
+        })?
+    }
+}
+
 impl Comparable for PyDict {
     fn cmp(
         zelf: &PyRef<Self>,
@@ -651,7 +685,7 @@ macro_rules! dict_iterator {
         }
 
         impl $name {
-            fn new(dict: PyDictRef) -> Self {
+            pub fn new(dict: PyDictRef) -> Self {
                 $name { dict }
             }
         }
@@ -901,26 +935,3 @@ pub(crate) fn init(context: &PyContext) {
     PyDictItemIterator::extend_class(context, &context.types.dict_itemiterator_type);
     PyDictReverseItemIterator::extend_class(context, &context.types.dict_reverseitemiterator_type);
 }
-
-pub struct PyMapping {
-    dict: PyDictRef,
-}
-
-impl TryFromObject for PyMapping {
-    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
-        let dict = vm.ctx.new_dict();
-        PyDict::merge(
-            &dict.entries,
-            OptionalArg::Present(obj),
-            KwArgs::default(),
-            vm,
-        )?;
-        Ok(PyMapping { dict })
-    }
-}
-
-impl PyMapping {
-    pub fn into_dict(self) -> PyDictRef {
-        self.dict
-    }
-}
diff --git a/vm/src/builtins/list.rs b/vm/src/builtins/list.rs
index 1f0fdfad58..bee377e7aa 100644
--- a/vm/src/builtins/list.rs
+++ b/vm/src/builtins/list.rs
@@ -8,11 +8,12 @@ use crate::common::lock::{
 };
 use crate::{
     function::{ArgIterable, FuncArgs, OptionalArg},
-    protocol::PyIterReturn,
+    protocol::{PyIterReturn, PyMappingMethods},
     sequence::{self, SimpleSeq},
     sliceable::{PySliceableSequence, PySliceableSequenceMut, SequenceIndex},
     slots::{
-        Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotIterator, Unhashable,
+        AsMapping, Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotIterator,
+        Unhashable,
     },
     utils::Either,
     vm::{ReprGuard, VirtualMachine},
@@ -82,7 +83,7 @@ pub(crate) struct SortOptions {
 
 pub type PyListRef = PyRef<PyList>;
 
-#[pyimpl(with(Iterable, Hashable, Comparable), flags(BASETYPE))]
+#[pyimpl(with(AsMapping, Iterable, Hashable, Comparable), flags(BASETYPE))]
 impl PyList {
     #[pymethod]
     pub(crate) fn append(&self, x: PyObjectRef) {
@@ -353,8 +354,8 @@ impl PyList {
     }
 
     #[pymethod(magic)]
-    fn delitem(&self, subscript: SequenceIndex, vm: &VirtualMachine) -> PyResult<()> {
-        match subscript {
+    fn delitem(&self, subscript: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
+        match SequenceIndex::try_from_object_for(vm, subscript, Self::NAME)? {
             SequenceIndex::Int(index) => self.delindex(index, vm),
             SequenceIndex::Slice(slice) => self.delslice(slice, vm),
         }
@@ -416,6 +417,39 @@ impl PyList {
     }
 }
 
+impl AsMapping for PyList {
+    fn as_mapping(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+        Ok(PyMappingMethods {
+            length: Some(Self::length),
+            subscript: Some(Self::subscript),
+            ass_subscript: Some(Self::ass_subscript),
+        })
+    }
+
+    #[inline]
+    fn length(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+        Self::downcast_ref(&zelf, vm).map(|zelf| Ok(zelf.len()))?
+    }
+
+    #[inline]
+    fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        Self::downcast(zelf, vm).map(|zelf| Self::getitem(zelf, needle, vm))?
+    }
+
+    #[inline]
+    fn ass_subscript(
+        zelf: PyObjectRef,
+        needle: PyObjectRef,
+        value: Option<PyObjectRef>,
+        vm: &VirtualMachine,
+    ) -> PyResult<()> {
+        Self::downcast_ref(&zelf, vm).map(|zelf| match value {
+            Some(value) => zelf.setitem(needle, value, vm),
+            None => zelf.delitem(needle, vm),
+        })?
+    }
+}
+
 impl Iterable for PyList {
     fn iter(zelf: PyRef<Self>, vm: &VirtualMachine) -> PyResult {
         Ok(PyListIterator {
diff --git a/vm/src/builtins/mappingproxy.rs b/vm/src/builtins/mappingproxy.rs
index fcf7d90716..225fd14326 100644
--- a/vm/src/builtins/mappingproxy.rs
+++ b/vm/src/builtins/mappingproxy.rs
@@ -1,9 +1,10 @@
-use super::{PyDict, PyStrRef, PyTypeRef};
+use super::{PyDict, PyList, PyStrRef, PyTuple, PyTypeRef};
 use crate::{
     function::OptionalArg,
-    slots::{Iterable, SlotConstructor},
+    protocol::{PyMapping, PyMappingMethods},
+    slots::{AsMapping, Iterable, SlotConstructor},
     IntoPyObject, ItemProtocol, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue,
-    TryFromObject, VirtualMachine,
+    TryFromObject, TypeProtocol, VirtualMachine,
 };
 
 #[pyclass(module = false, name = "mappingproxy")]
@@ -36,14 +37,24 @@ impl SlotConstructor for PyMappingProxy {
     type Args = PyObjectRef;
 
     fn py_new(cls: PyTypeRef, mapping: Self::Args, vm: &VirtualMachine) -> PyResult {
-        Self {
-            mapping: MappingProxyInner::Dict(mapping),
+        if !PyMapping::check(&mapping)
+            || mapping.payload_if_subclass::<PyList>(vm).is_some()
+            || mapping.payload_if_subclass::<PyTuple>(vm).is_some()
+        {
+            Err(vm.new_type_error(format!(
+                "mappingproxy() argument must be a mapping, not {}",
+                mapping.class()
+            )))
+        } else {
+            Self {
+                mapping: MappingProxyInner::Dict(mapping),
+            }
+            .into_pyresult_with_type(vm, cls)
         }
-        .into_pyresult_with_type(vm, cls)
     }
 }
 
-#[pyimpl(with(Iterable, SlotConstructor))]
+#[pyimpl(with(AsMapping, Iterable, SlotConstructor))]
 impl PyMappingProxy {
     fn get_inner(&self, key: PyObjectRef, vm: &VirtualMachine) -> PyResult<Option<PyObjectRef>> {
         let opt = match &self.mapping {
@@ -127,6 +138,37 @@ impl PyMappingProxy {
         }
     }
 }
+
+impl AsMapping for PyMappingProxy {
+    fn as_mapping(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+        Ok(PyMappingMethods {
+            length: None,
+            subscript: Some(Self::subscript),
+            ass_subscript: None,
+        })
+    }
+
+    #[inline]
+    fn length(zelf: PyObjectRef, _vm: &VirtualMachine) -> PyResult<usize> {
+        unreachable!("length not implemented for {}", zelf.class())
+    }
+
+    #[inline]
+    fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        Self::downcast_ref(&zelf, vm).map(|zelf| zelf.getitem(needle, vm))?
+    }
+
+    #[cold]
+    fn ass_subscript(
+        zelf: PyObjectRef,
+        _needle: PyObjectRef,
+        _value: Option<PyObjectRef>,
+        _vm: &VirtualMachine,
+    ) -> PyResult<()> {
+        unreachable!("ass_subscript not implemented for {}", zelf.class())
+    }
+}
+
 impl Iterable for PyMappingProxy {
     fn iter(zelf: PyRef<Self>, vm: &VirtualMachine) -> PyResult {
         let obj = match &zelf.mapping {
diff --git a/vm/src/builtins/memory.rs b/vm/src/builtins/memory.rs
index eaf8539c77..1dd313dd44 100644
--- a/vm/src/builtins/memory.rs
+++ b/vm/src/builtins/memory.rs
@@ -8,13 +8,13 @@ use crate::common::{
 use crate::{
     bytesinner::bytes_to_hex,
     function::{FuncArgs, OptionalArg},
-    protocol::{BufferInternal, BufferOptions, PyBuffer},
+    protocol::{BufferInternal, BufferOptions, PyBuffer, PyMappingMethods},
     sliceable::{convert_slice, wrap_index, SequenceIndex},
-    slots::{AsBuffer, Comparable, Hashable, PyComparisonOp, SlotConstructor},
+    slots::{AsBuffer, AsMapping, Comparable, Hashable, PyComparisonOp, SlotConstructor},
     stdlib::pystruct::FormatSpec,
     utils::Either,
-    IdProtocol, IntoPyObject, PyClassImpl, PyComparisonValue, PyContext, PyObjectRef, PyRef,
-    PyResult, PyValue, TryFromBorrowedObject, TryFromObject, TypeProtocol, VirtualMachine,
+    IdProtocol, IntoPyObject, PyClassDef, PyClassImpl, PyComparisonValue, PyContext, PyObjectRef,
+    PyRef, PyResult, PyValue, TryFromBorrowedObject, TryFromObject, TypeProtocol, VirtualMachine,
 };
 use crossbeam_utils::atomic::AtomicCell;
 use itertools::Itertools;
@@ -53,7 +53,7 @@ impl SlotConstructor for PyMemoryView {
     }
 }
 
-#[pyimpl(with(Hashable, Comparable, AsBuffer, SlotConstructor))]
+#[pyimpl(with(Hashable, Comparable, AsBuffer, AsMapping, SlotConstructor))]
 impl PyMemoryView {
     #[cfg(debug_assertions)]
     fn validate(self) -> Self {
@@ -342,10 +342,10 @@ impl PyMemoryView {
     }
 
     #[pymethod(magic)]
-    fn getitem(zelf: PyRef<Self>, needle: SequenceIndex, vm: &VirtualMachine) -> PyResult {
+    fn getitem(zelf: PyRef<Self>, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
         zelf.try_not_released(vm)?;
-        match needle {
-            SequenceIndex::Int(i) => Self::getitem_by_idx(zelf, i, vm),
+        match SequenceIndex::try_from_object_for(vm, needle, Self::NAME)? {
+            SequenceIndex::Int(index) => Self::getitem_by_idx(zelf, index, vm),
             SequenceIndex::Slice(slice) => Self::getitem_by_slice(zelf, slice, vm),
         }
     }
@@ -459,7 +459,7 @@ impl PyMemoryView {
     #[pymethod(magic)]
     fn setitem(
         zelf: PyRef<Self>,
-        needle: SequenceIndex,
+        needle: PyObjectRef,
         value: PyObjectRef,
         vm: &VirtualMachine,
     ) -> PyResult<()> {
@@ -467,8 +467,8 @@ impl PyMemoryView {
         if zelf.buffer.options.readonly {
             return Err(vm.new_type_error("cannot modify read-only memory".to_owned()));
         }
-        match needle {
-            SequenceIndex::Int(i) => Self::setitem_by_idx(zelf, i, value, vm),
+        match SequenceIndex::try_from_object_for(vm, needle, Self::NAME)? {
+            SequenceIndex::Int(index) => Self::setitem_by_idx(zelf, index, value, vm),
             SequenceIndex::Slice(slice) => Self::setitem_by_slice(zelf, slice, value, vm),
         }
     }
@@ -734,6 +734,41 @@ impl BufferInternal for PyRef<PyMemoryView> {
     fn retain(&self) {}
 }
 
+impl AsMapping for PyMemoryView {
+    fn as_mapping(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+        Ok(PyMappingMethods {
+            length: Some(Self::length),
+            subscript: Some(Self::subscript),
+            ass_subscript: Some(Self::ass_subscript),
+        })
+    }
+
+    #[inline]
+    fn length(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+        Self::downcast_ref(&zelf, vm).map(|zelf| zelf.len(vm))?
+    }
+
+    #[inline]
+    fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        Self::downcast(zelf, vm).map(|zelf| Self::getitem(zelf, needle, vm))?
+    }
+
+    #[inline]
+    fn ass_subscript(
+        zelf: PyObjectRef,
+        needle: PyObjectRef,
+        value: Option<PyObjectRef>,
+        vm: &VirtualMachine,
+    ) -> PyResult<()> {
+        match value {
+            Some(value) => {
+                Self::downcast(zelf, vm).map(|zelf| Self::setitem(zelf, needle, value, vm))?
+            }
+            None => Err(vm.new_type_error("cannot delete memory".to_owned())),
+        }
+    }
+}
+
 impl Comparable for PyMemoryView {
     fn cmp(
         zelf: &PyRef<Self>,
diff --git a/vm/src/builtins/pytype.rs b/vm/src/builtins/pytype.rs
index b9f67d096d..9db1530c8a 100644
--- a/vm/src/builtins/pytype.rs
+++ b/vm/src/builtins/pytype.rs
@@ -5,13 +5,14 @@ use super::{
 use crate::common::{ascii, lock::PyRwLock};
 use crate::{
     function::{FuncArgs, KwArgs, OptionalArg},
-    protocol::PyIterReturn,
+    protocol::{PyIterReturn, PyMappingMethods},
     slots::{self, Callable, PyTypeFlags, PyTypeSlots, SlotGetattro, SlotSetattro},
     utils::Either,
     IdProtocol, PyAttributes, PyClassImpl, PyContext, PyLease, PyObjectRef, PyRef, PyResult,
     PyValue, TryFromObject, TypeProtocol, VirtualMachine,
 };
 use itertools::Itertools;
+use num_traits::ToPrimitive;
 use std::collections::HashSet;
 use std::fmt;
 use std::ops::Deref;
@@ -270,6 +271,54 @@ impl PyType {
                 };
                 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: slots::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
+            }
             _ => {}
         }
     }
diff --git a/vm/src/builtins/range.rs b/vm/src/builtins/range.rs
index 4f6db0a594..6c9d0a0dbb 100644
--- a/vm/src/builtins/range.rs
+++ b/vm/src/builtins/range.rs
@@ -2,8 +2,10 @@ use super::{PyInt, PyIntRef, PySlice, PySliceRef, PyTypeRef};
 use crate::common::hash::PyHash;
 use crate::{
     function::{FuncArgs, OptionalArg},
-    protocol::PyIterReturn,
-    slots::{Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotIterator},
+    protocol::{PyIterReturn, PyMappingMethods},
+    slots::{
+        AsMapping, Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotIterator,
+    },
     IdProtocol, IntoPyRef, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue,
     TryFromObject, TypeProtocol, VirtualMachine,
 };
@@ -98,7 +100,7 @@ impl PyRange {
 
     #[inline]
     pub fn is_empty(&self) -> bool {
-        self.length().is_zero()
+        self.compute_length().is_zero()
     }
 
     #[inline]
@@ -116,7 +118,7 @@ impl PyRange {
         }
 
         if index.is_negative() {
-            let length = self.length();
+            let length = self.compute_length();
             let index: BigInt = &length + index;
             if index.is_negative() {
                 return None;
@@ -143,7 +145,7 @@ impl PyRange {
     }
 
     #[inline]
-    fn length(&self) -> BigInt {
+    fn compute_length(&self) -> BigInt {
         let start = self.start.as_bigint();
         let stop = self.stop.as_bigint();
         let step = self.step.as_bigint();
@@ -173,7 +175,7 @@ pub fn init(context: &PyContext) {
     PyRangeIterator::extend_class(context, &context.types.range_iterator_type);
 }
 
-#[pyimpl(with(Hashable, Comparable, Iterable))]
+#[pyimpl(with(AsMapping, Hashable, Comparable, Iterable))]
 impl PyRange {
     fn new(cls: PyTypeRef, stop: PyIntRef, vm: &VirtualMachine) -> PyResult<PyRef<Self>> {
         PyRange {
@@ -251,7 +253,7 @@ impl PyRange {
 
     #[pymethod(magic)]
     fn len(&self) -> BigInt {
-        self.length()
+        self.compute_length()
     }
 
     #[pymethod(magic)]
@@ -331,11 +333,11 @@ impl PyRange {
     }
 
     #[pymethod(magic)]
-    fn getitem(&self, subscript: RangeIndex, vm: &VirtualMachine) -> PyResult {
-        match subscript {
+    fn getitem(&self, subscript: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        match RangeIndex::try_from_object(vm, subscript)? {
             RangeIndex::Slice(slice) => {
                 let (mut substart, mut substop, mut substep) =
-                    slice.inner_indices(&self.length(), vm)?;
+                    slice.inner_indices(&self.compute_length(), vm)?;
                 let range_step = &self.step;
                 let range_start = &self.start;
 
@@ -372,9 +374,39 @@ impl PyRange {
     }
 }
 
+impl AsMapping for PyRange {
+    fn as_mapping(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+        Ok(PyMappingMethods {
+            length: Some(Self::length),
+            subscript: Some(Self::subscript),
+            ass_subscript: None,
+        })
+    }
+
+    #[inline]
+    fn length(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+        Self::downcast_ref(&zelf, vm).map(|zelf| Ok(zelf.len().to_usize().unwrap()))?
+    }
+
+    #[inline]
+    fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        Self::downcast_ref(&zelf, vm).map(|zelf| zelf.getitem(needle, vm))?
+    }
+
+    #[inline]
+    fn ass_subscript(
+        zelf: PyObjectRef,
+        _needle: PyObjectRef,
+        _value: Option<PyObjectRef>,
+        _vm: &VirtualMachine,
+    ) -> PyResult<()> {
+        unreachable!("ass_subscript not implemented for {}", zelf.class())
+    }
+}
+
 impl Hashable for PyRange {
     fn hash(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyHash> {
-        let length = zelf.length();
+        let length = zelf.compute_length();
         let elements = if length.is_zero() {
             [vm.ctx.new_int(length), vm.ctx.none(), vm.ctx.none()]
         } else if length.is_one() {
@@ -406,8 +438,8 @@ impl Comparable for PyRange {
                 return Ok(true.into());
             }
             let rhs = class_or_notimplemented!(Self, other);
-            let lhs_len = zelf.length();
-            let eq = if lhs_len != rhs.length() {
+            let lhs_len = zelf.compute_length();
+            let eq = if lhs_len != rhs.compute_length() {
                 false
             } else if lhs_len.is_zero() {
                 true
diff --git a/vm/src/builtins/tuple.rs b/vm/src/builtins/tuple.rs
index 03c11d4e50..3f5e8e51df 100644
--- a/vm/src/builtins/tuple.rs
+++ b/vm/src/builtins/tuple.rs
@@ -6,12 +6,12 @@ use super::{
 use crate::common::hash::PyHash;
 use crate::{
     function::OptionalArg,
-    protocol::PyIterReturn,
+    protocol::{PyIterReturn, PyMappingMethods},
     sequence::{self, SimpleSeq},
     sliceable::PySliceableSequence,
     slots::{
-        Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotConstructor,
-        SlotIterator,
+        AsMapping, Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp,
+        SlotConstructor, SlotIterator,
     },
     utils::Either,
     vm::{ReprGuard, VirtualMachine},
@@ -111,7 +111,10 @@ impl SlotConstructor for PyTuple {
     }
 }
 
-#[pyimpl(flags(BASETYPE), with(Hashable, Comparable, Iterable, SlotConstructor))]
+#[pyimpl(
+    flags(BASETYPE),
+    with(AsMapping, Hashable, Comparable, Iterable, SlotConstructor)
+)]
 impl PyTuple {
     /// Creating a new tuple with given boxed slice.
     /// NOTE: for usual case, you probably want to use PyTupleRef::with_elements.
@@ -284,6 +287,36 @@ impl PyTuple {
     }
 }
 
+impl AsMapping for PyTuple {
+    fn as_mapping(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+        Ok(PyMappingMethods {
+            length: Some(Self::length),
+            subscript: Some(Self::subscript),
+            ass_subscript: None,
+        })
+    }
+
+    #[inline]
+    fn length(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
+        Self::downcast_ref(&zelf, vm).map(|zelf| Ok(zelf.len()))?
+    }
+
+    #[inline]
+    fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        Self::downcast(zelf, vm).map(|zelf| Self::getitem(zelf, needle, vm))?
+    }
+
+    #[inline]
+    fn ass_subscript(
+        zelf: PyObjectRef,
+        _needle: PyObjectRef,
+        _value: Option<PyObjectRef>,
+        _vm: &VirtualMachine,
+    ) -> PyResult<()> {
+        unreachable!("ass_subscript not implemented for {}", zelf.class())
+    }
+}
+
 impl Hashable for PyTuple {
     fn hash(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyHash> {
         crate::utils::hash_iter(zelf.elements.iter(), vm)
diff --git a/vm/src/protocol/mapping.rs b/vm/src/protocol/mapping.rs
new file mode 100644
index 0000000000..bf832cf1f7
--- /dev/null
+++ b/vm/src/protocol/mapping.rs
@@ -0,0 +1,135 @@
+use crate::{
+    builtins::dict::{PyDictKeys, PyDictRef, PyDictValues},
+    builtins::list::PyList,
+    vm::VirtualMachine,
+    IdProtocol, IntoPyObject, PyObjectRef, PyResult, TryFromObject, TypeProtocol,
+};
+use std::borrow::Borrow;
+use std::ops::Deref;
+
+// Mapping protocol
+// https://docs.python.org/3/c-api/mapping.html
+#[allow(clippy::type_complexity)]
+#[derive(Default)]
+pub struct PyMappingMethods {
+    pub length: Option<fn(PyObjectRef, &VirtualMachine) -> PyResult<usize>>,
+    pub subscript: Option<fn(PyObjectRef, PyObjectRef, &VirtualMachine) -> PyResult>,
+    pub ass_subscript:
+        Option<fn(PyObjectRef, PyObjectRef, Option<PyObjectRef>, &VirtualMachine) -> PyResult<()>>,
+}
+
+#[derive(Debug, Clone)]
+#[repr(transparent)]
+pub struct PyMapping<T = PyObjectRef>(T)
+where
+    T: Borrow<PyObjectRef>;
+
+impl PyMapping<PyObjectRef> {
+    pub fn into_object(self) -> PyObjectRef {
+        self.0
+    }
+
+    pub fn check(obj: &PyObjectRef) -> bool {
+        obj.class()
+            .mro_find_map(|x| x.slots.as_mapping.load())
+            .is_some()
+    }
+
+    pub fn methods(&self, vm: &VirtualMachine) -> PyMappingMethods {
+        let obj_cls = self.0.class();
+        for cls in obj_cls.iter_mro() {
+            if let Some(f) = cls.slots.as_mapping.load() {
+                return f(&self.0, vm).unwrap();
+            }
+        }
+        PyMappingMethods::default()
+    }
+}
+
+impl<T> PyMapping<T>
+where
+    T: Borrow<PyObjectRef>,
+{
+    pub fn new(obj: T) -> Self {
+        Self(obj)
+    }
+
+    pub fn keys(&self, vm: &VirtualMachine) -> PyResult {
+        if self.0.borrow().is(&vm.ctx.types.dict_type) {
+            Ok(
+                PyDictKeys::new(PyDictRef::try_from_object(vm, self.0.borrow().clone())?)
+                    .into_pyobject(vm),
+            )
+        } else {
+            Self::method_output_as_list(self.0.borrow(), "keys", vm)
+        }
+    }
+
+    pub fn values(&self, vm: &VirtualMachine) -> PyResult {
+        if self.0.borrow().is(&vm.ctx.types.dict_type) {
+            Ok(
+                PyDictValues::new(PyDictRef::try_from_object(vm, self.0.borrow().clone())?)
+                    .into_pyobject(vm),
+            )
+        } else {
+            Self::method_output_as_list(self.0.borrow(), "values", vm)
+        }
+    }
+
+    fn method_output_as_list(
+        obj: &PyObjectRef,
+        method_name: &str,
+        vm: &VirtualMachine,
+    ) -> PyResult {
+        let meth_output = vm.call_method(obj, method_name, ())?;
+        if meth_output.is(&vm.ctx.types.list_type) {
+            return Ok(meth_output);
+        }
+
+        let iter = meth_output.clone().get_iter(vm).map_err(|_| {
+            vm.new_type_error(format!(
+                "{}.{}() returned a non-iterable (type {})",
+                obj.class(),
+                method_name,
+                meth_output.class()
+            ))
+        })?;
+
+        Ok(PyList::from(vm.extract_elements(&iter)?).into_pyobject(vm))
+    }
+}
+
+impl<T> Borrow<PyObjectRef> for PyMapping<T>
+where
+    T: Borrow<PyObjectRef>,
+{
+    fn borrow(&self) -> &PyObjectRef {
+        self.0.borrow()
+    }
+}
+
+impl<T> Deref for PyMapping<T>
+where
+    T: Borrow<PyObjectRef>,
+{
+    type Target = PyObjectRef;
+    fn deref(&self) -> &Self::Target {
+        self.0.borrow()
+    }
+}
+
+impl IntoPyObject for PyMapping<PyObjectRef> {
+    fn into_pyobject(self, _vm: &VirtualMachine) -> PyObjectRef {
+        self.into_object()
+    }
+}
+
+impl TryFromObject for PyMapping<PyObjectRef> {
+    fn try_from_object(vm: &VirtualMachine, mapping: PyObjectRef) -> PyResult<Self> {
+        if Self::check(&mapping) {
+            Ok(Self::new(mapping))
+        } else {
+            Err(vm.new_type_error(format!("{} is not a mapping object", mapping.class())))
+        }
+    }
+}
diff --git a/vm/src/protocol/mod.rs b/vm/src/protocol/mod.rs
index 0c44ab7545..548eaaee12 100644
--- a/vm/src/protocol/mod.rs
+++ b/vm/src/protocol/mod.rs
@@ -1,5 +1,7 @@
 mod buffer;
 mod iter;
+mod mapping;
 
 pub use buffer::{BufferInternal, BufferOptions, PyBuffer, ResizeGuard};
 pub use iter::{PyIter, PyIterReturn};
+pub use mapping::{PyMapping, PyMappingMethods};
diff --git a/vm/src/pyobject.rs b/vm/src/pyobject.rs
index 514a88823a..b51e5a000d 100644
--- a/vm/src/pyobject.rs
+++ b/vm/src/pyobject.rs
@@ -20,6 +20,7 @@ use crate::{
     dictdatatype::Dict,
     exceptions,
     function::{IntoFuncArgs, IntoPyNativeFunc},
+    protocol::PyMapping,
     slots::{PyTypeFlags, PyTypeSlots},
     types::{create_type_with_slots, TypeZoo},
     VirtualMachine,
@@ -639,6 +640,12 @@ where
     T: IntoPyObject,
 {
     fn get_item(&self, key: T, vm: &VirtualMachine) -> PyResult {
+        if let Ok(mapping) = PyMapping::try_from_object(vm, self.clone()) {
+            if let Some(getitem) = mapping.methods(vm).subscript {
+                return getitem(self.clone(), key.into_pyobject(vm), vm);
+            }
+        }
+
         match vm.get_special_method(self.clone(), "__getitem__")? {
             Ok(special_method) => return special_method.invoke((key,), vm),
             Err(obj) => {
@@ -656,6 +663,12 @@ where
     }
 
     fn set_item(&self, key: T, value: PyObjectRef, vm: &VirtualMachine) -> PyResult<()> {
+        if let Ok(mapping) = PyMapping::try_from_object(vm, self.clone()) {
+            if let Some(setitem) = mapping.methods(vm).ass_subscript {
+                return setitem(self.clone(), key.into_pyobject(vm), Some(value), vm);
+            }
+        }
+
         vm.get_special_method(self.clone(), "__setitem__")?
             .map_err(|obj| {
                 vm.new_type_error(format!(
@@ -668,6 +681,12 @@ where
     }
 
     fn del_item(&self, key: T, vm: &VirtualMachine) -> PyResult<()> {
+        if let Ok(mapping) = PyMapping::try_from_object(vm, self.clone()) {
+            if let Some(setitem) = mapping.methods(vm).ass_subscript {
+                return setitem(self.clone(), key.into_pyobject(vm), None, vm);
+            }
+        }
+
         vm.get_special_method(self.clone(), "__delitem__")?
             .map_err(|obj| {
                 vm.new_type_error(format!(
diff --git a/vm/src/slots.rs b/vm/src/slots.rs
index 37382e6ecd..99c25264e3 100644
--- a/vm/src/slots.rs
+++ b/vm/src/slots.rs
@@ -2,7 +2,7 @@ use crate::builtins::{PyStrRef, PyTypeRef};
 use crate::common::hash::PyHash;
 use crate::common::lock::PyRwLock;
 use crate::function::{FromArgs, FuncArgs, OptionalArg};
-use crate::protocol::{PyBuffer, PyIterReturn};
+use crate::protocol::{PyBuffer, PyIterReturn, PyMappingMethods};
 use crate::utils::Either;
 use crate::VirtualMachine;
 use crate::{
@@ -70,6 +70,7 @@ pub(crate) type GetattroFunc = fn(PyObjectRef, PyStrRef, &VirtualMachine) -> PyR
 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>;
 
@@ -85,7 +86,7 @@ pub struct PyTypeSlots {
     // Method suites for standard classes
     // tp_as_number
     // tp_as_sequence
-    // tp_as_mapping
+    pub as_mapping: AtomicCell<Option<MappingFunc>>,
 
     // More standard operations (here for binary compatibility)
     pub hash: AtomicCell<Option<HashFunc>>,
@@ -532,6 +533,50 @@ pub trait AsBuffer: PyValue {
     fn as_buffer(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyBuffer>;
 }
 
+#[pyimpl]
+pub trait AsMapping: PyValue {
+    #[pyslot]
+    fn slot_as_mapping(zelf: &PyObjectRef, vm: &VirtualMachine) -> PyResult<PyMappingMethods> {
+        let zelf = zelf
+            .downcast_ref()
+            .ok_or_else(|| vm.new_type_error("unexpected payload for as_mapping".to_owned()))?;
+        Self::as_mapping(zelf, vm)
+    }
+
+    fn downcast(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<PyRef<Self>> {
+        zelf.downcast::<Self>().map_err(|obj| {
+            vm.new_type_error(format!(
+                "{} type is required, not {}",
+                Self::class(vm),
+                obj.class()
+            ))
+        })
+    }
+
+    fn downcast_ref<'a>(zelf: &'a PyObjectRef, vm: &VirtualMachine) -> PyResult<&'a PyRef<Self>> {
+        zelf.downcast_ref::<Self>().ok_or_else(|| {
+            vm.new_type_error(format!(
+                "{} type is required, not {}",
+                Self::class(vm),
+                zelf.class()
+            ))
+        })
+    }
+
+    fn as_mapping(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyMappingMethods>;
+
+    fn length(zelf: PyObjectRef, _vm: &VirtualMachine) -> PyResult<usize>;
+
+    fn subscript(zelf: PyObjectRef, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult;
+
+    fn ass_subscript(
+        zelf: PyObjectRef,
+        needle: PyObjectRef,
+        value: Option<PyObjectRef>,
+        vm: &VirtualMachine,
+    ) -> PyResult<()>;
+}
+
 #[pyimpl]
 pub trait Iterable: PyValue {
     #[pyslot]
diff --git a/vm/src/stdlib/posix.rs b/vm/src/stdlib/posix.rs
index 58f10618e1..ae6251a5a7 100644
--- a/vm/src/stdlib/posix.rs
+++ b/vm/src/stdlib/posix.rs
@@ -1049,8 +1049,24 @@ pub mod module {
     }
 
     #[cfg(any(target_os = "linux", target_os = "freebsd", target_os = "macos"))]
-    fn envp_from_dict(dict: PyDictRef, vm: &VirtualMachine) -> PyResult<Vec<CString>> {
-        dict.into_iter()
+    fn envp_from_dict(
+        env: crate::protocol::PyMapping,
+        vm: &VirtualMachine,
+    ) -> PyResult<Vec<CString>> {
+        let keys = env.keys(vm)?;
+        let values = env.values(vm)?;
+
+        let keys = PyListRef::try_from_object(vm, keys)
+            .map_err(|_| vm.new_type_error("env.keys() is not a list".to_owned()))?
+            .borrow_vec()
+            .to_vec();
+        let values = PyListRef::try_from_object(vm, values)
+            .map_err(|_| vm.new_type_error("env.values() is not a list".to_owned()))?
+            .borrow_vec()
+            .to_vec();
+
+        keys.into_iter()
+            .zip(values.into_iter())
             .map(|(k, v)| {
                 let k = PyPathLike::try_from_object(vm, k)?.into_bytes();
                 let v = PyPathLike::try_from_object(vm, v)?.into_bytes();
@@ -1085,7 +1101,7 @@ pub mod module {
         #[pyarg(positional)]
         args: crate::function::ArgIterable<PyPathLike>,
         #[pyarg(positional)]
-        env: crate::builtins::dict::PyMapping,
+        env: crate::protocol::PyMapping,
         #[pyarg(named, default)]
         file_actions: Option<crate::function::ArgIterable<PyTupleRef>>,
         #[pyarg(named, default)]
@@ -1198,7 +1214,7 @@ pub mod module {
                 .map(|s| s.as_ptr() as _)
                 .chain(std::iter::once(std::ptr::null_mut()))
                 .collect();
-            let mut env = envp_from_dict(self.env.into_dict(), vm)?;
+            let mut env = envp_from_dict(self.env, vm)?;
             let envp: Vec<*mut libc::c_char> = env
                 .iter_mut()
                 .map(|s| s.as_ptr() as _)
diff --git a/vm/src/stdlib/winapi.rs b/vm/src/stdlib/winapi.rs
index 5ca3e20712..1ce91a8378 100644
--- a/vm/src/stdlib/winapi.rs
+++ b/vm/src/stdlib/winapi.rs
@@ -2,10 +2,11 @@
 
 use super::os::errno_err;
 use crate::{
-    builtins::{dict::PyMapping, PyDictRef, PyStrRef},
+    builtins::{PyListRef, PyStrRef},
     exceptions::IntoPyException,
     function::OptionalArg,
-    PyObjectRef, PyResult, PySequence, TryFromObject, VirtualMachine,
+    protocol::PyMapping,
+    ItemProtocol, PyObjectRef, PyResult, PySequence, TryFromObject, VirtualMachine,
 };
 use std::ptr::{null, null_mut};
 use winapi::shared::winerror;
@@ -155,7 +156,7 @@ fn _winapi_CreateProcess(
 
     let mut env = args
         .env_mapping
-        .map(|m| getenvironment(m.into_dict(), vm))
+        .map(|m| getenvironment(m, vm))
         .transpose()?;
     let env = env.as_mut().map_or_else(null_mut, |v| v.as_mut_ptr());
 
@@ -216,9 +217,21 @@ fn _winapi_CreateProcess(
     ))
 }
 
-fn getenvironment(env: PyDictRef, vm: &VirtualMachine) -> PyResult<Vec<u16>> {
+fn getenvironment(env: PyMapping, vm: &VirtualMachine) -> PyResult<Vec<u16>> {
+    let keys = env.keys(vm)?;
+    let values = env.values(vm)?;
+
+    let keys = PyListRef::try_from_object(vm, keys)?.borrow_vec().to_vec();
+    let values = PyListRef::try_from_object(vm, values)?
+        .borrow_vec()
+        .to_vec();
+
+    if keys.len() != values.len() {
+        return Err(vm.new_runtime_error("environment changed size during iteration".to_owned()));
+    }
+
     let mut out = widestring::WideString::new();
-    for (k, v) in env {
+    for (k, v) in keys.into_iter().zip(values.into_iter()) {
         let k = PyStrRef::try_from_object(vm, k)?;
         let k = k.as_str();
         let v = PyStrRef::try_from_object(vm, v)?;
@@ -252,10 +265,11 @@ impl Drop for AttrList {
 
 fn getattributelist(obj: PyObjectRef, vm: &VirtualMachine) -> PyResult<Option<AttrList>> {
     <Option<PyMapping>>::try_from_object(vm, obj)?
-        .map(|d| {
-            let d = d.into_dict();
-            let handlelist = d
-                .get_item_option("handle_list", vm)?
+        .map(|mapping| {
+            let handlelist = mapping
+                .into_object()
+                .get_item("handle_list", vm)
+                .ok()
                 .and_then(|obj| {
                     <Option<PySequence<usize>>>::try_from_object(vm, obj)
                         .map(|s| match s {
@@ -265,6 +279,7 @@ fn getattributelist(obj: PyObjectRef, vm: &VirtualMachine) -> PyResult<Option<At
                         .transpose()
                 })
                 .transpose()?;
+
             let attr_count = handlelist.is_some() as u32;
             let mut size = 0;
             let ret = unsafe {