PyIterReturn for StopIteration

Same as ArithmaticValue for NotImplemented

extra_tests/snippets/builtin_filter.py

@@ -29,4 +29,5 @@ def predicate(x):
     return True
 
 
-assert list(filter(predicate, [1, 2, 0, 4, 5])) == [1, 2]
+filtered = list(filter(predicate, [1, 2, 0, 4, 5]))
+assert filtered == [1, 2], filtered

stdlib/src/array.rs

@@ -17,7 +17,7 @@ mod array {
         },
         class_or_notimplemented,
         function::{ArgBytesLike, ArgIterable, OptionalArg},
-        protocol::{BufferInternal, BufferOptions, PyBuffer, ResizeGuard},
+        protocol::{BufferInternal, BufferOptions, PyBuffer, PyIterReturn, ResizeGuard},
         sliceable::{saturate_index, PySliceableSequence, PySliceableSequenceMut, SequenceIndex},
         slots::{
             AsBuffer, Comparable, Iterable, IteratorIterable, PyComparisonOp, SlotConstructor,
@@ -1199,13 +1199,14 @@ mod array {
 
     impl IteratorIterable for PyArrayIter {}
     impl SlotIterator for PyArrayIter {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let pos = zelf.position.fetch_add(1);
-            if let Some(item) = zelf.array.read().getitem_by_idx(pos, vm)? {
-                Ok(item)
+            let r = if let Some(item) = zelf.array.read().getitem_by_idx(pos, vm)? {
+                PyIterReturn::Return(item)
             } else {
-                Err(vm.new_stop_iteration())
-            }
+                PyIterReturn::StopIteration(None)
+            };
+            Ok(r)
         }
     }
 

stdlib/src/csv.rs

@@ -3,7 +3,7 @@ use crate::vm::{
     builtins::{PyStr, PyStrRef},
     function::{ArgIterable, ArgumentError, FromArgs, FuncArgs},
     match_class, named_function,
-    protocol::PyIter,
+    protocol::{PyIter, PyIterReturn},
     py_module,
     slots::{IteratorIterable, SlotIterator},
     types::create_simple_type,
@@ -101,8 +101,11 @@ impl fmt::Debug for Reader {
 impl Reader {}
 impl IteratorIterable for Reader {}
 impl SlotIterator for Reader {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        let string = zelf.iter.next(vm)?;
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+        let string = match zelf.iter.next(vm)? {
+            PyIterReturn::Return(obj) => obj,
+            PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+        };
         let string = string.downcast::<PyStr>().map_err(|obj| {
             vm.new_type_error(format!(
                 "iterator should return strings, not {} (the file should be opened in text mode)",
@@ -136,7 +139,7 @@ impl SlotIterator for Reader {
                 csv_core::ReadRecordResult::OutputFull => resize_buf(buffer),
                 csv_core::ReadRecordResult::OutputEndsFull => resize_buf(output_ends),
                 csv_core::ReadRecordResult::Record => break,
-                csv_core::ReadRecordResult::End => return Err(vm.new_stop_iteration()),
+                csv_core::ReadRecordResult::End => return Ok(PyIterReturn::StopIteration(None)),
             }
         }
         let rest = &input[input_offset..];
@@ -160,7 +163,7 @@ impl SlotIterator for Reader {
                     .map_err(|_e| vm.new_unicode_decode_error("csv not utf8".to_owned()))
             })
             .collect::<Result<_, _>>()?;
-        Ok(vm.ctx.new_list(out))
+        Ok(PyIterReturn::Return(vm.ctx.new_list(out)))
     }
 }
 

vm/src/builtins/asyncgenerator.rs

@@ -4,6 +4,7 @@ use crate::{
     coroutine::{Coro, Variant},
     frame::FrameRef,
     function::OptionalArg,
+    protocol::PyIterReturn,
     slots::{IteratorIterable, SlotIterator},
     IdProtocol, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue, TypeProtocol,
     VirtualMachine,
@@ -256,8 +257,9 @@ impl PyAsyncGenASend {
 
 impl IteratorIterable for PyAsyncGenASend {}
 impl SlotIterator for PyAsyncGenASend {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        zelf.send(vm.ctx.none(), vm)
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+        // TODO: Fix zelf.send to return PyIterReturn
+        PyIterReturn::from_result(zelf.send(vm.ctx.none(), vm), vm)
     }
 }
 
@@ -398,8 +400,9 @@ impl PyAsyncGenAThrow {
 
 impl IteratorIterable for PyAsyncGenAThrow {}
 impl SlotIterator for PyAsyncGenAThrow {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        zelf.send(vm.ctx.none(), vm)
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+        // TODO: Fix zelf.send to return PyIterReturn
+        PyIterReturn::from_result(zelf.send(vm.ctx.none(), vm), vm)
     }
 }
 

vm/src/builtins/bytearray.rs

@@ -15,7 +15,7 @@ use crate::{
         ByteInnerTranslateOptions, DecodeArgs, PyBytesInner,
     },
     function::{ArgBytesLike, ArgIterable, FuncArgs, OptionalArg, OptionalOption},
-    protocol::{BufferInternal, BufferOptions, PyBuffer, ResizeGuard},
+    protocol::{BufferInternal, BufferOptions, PyBuffer, PyIterReturn, ResizeGuard},
     sliceable::{PySliceableSequence, PySliceableSequenceMut, SequenceIndex},
     slots::{
         AsBuffer, Callable, Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp,
@@ -745,12 +745,13 @@ impl PyValue for PyByteArrayIterator {
 impl PyByteArrayIterator {}
 impl IteratorIterable for PyByteArrayIterator {}
 impl SlotIterator for PyByteArrayIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         let pos = zelf.position.fetch_add(1);
-        if let Some(&ret) = zelf.bytearray.borrow_buf().get(pos) {
-            Ok(ret.into_pyobject(vm))
+        let r = if let Some(&ret) = zelf.bytearray.borrow_buf().get(pos) {
+            PyIterReturn::Return(ret.into_pyobject(vm))
         } else {
-            Err(vm.new_stop_iteration())
-        }
+            PyIterReturn::StopIteration(None)
+        };
+        Ok(r)
     }
 }

vm/src/builtins/bytes.rs

@@ -7,7 +7,7 @@ use crate::{
     },
     common::hash::PyHash,
     function::{ArgBytesLike, ArgIterable, OptionalArg, OptionalOption},
-    protocol::{BufferInternal, BufferOptions, PyBuffer},
+    protocol::{BufferInternal, BufferOptions, PyBuffer, PyIterReturn},
     slots::{
         AsBuffer, Callable, Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp,
         SlotConstructor, SlotIterator,
@@ -598,13 +598,14 @@ impl PyValue for PyBytesIterator {
 impl PyBytesIterator {}
 impl IteratorIterable for PyBytesIterator {}
 impl SlotIterator for PyBytesIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         let pos = zelf.position.fetch_add(1);
-        if let Some(&ret) = zelf.bytes.as_bytes().get(pos) {
-            Ok(vm.ctx.new_int(ret))
+        let r = if let Some(&ret) = zelf.bytes.as_bytes().get(pos) {
+            PyIterReturn::Return(vm.ctx.new_int(ret))
         } else {
-            Err(vm.new_stop_iteration())
-        }
+            PyIterReturn::StopIteration(None)
+        };
+        Ok(r)
     }
 }
 

vm/src/builtins/coroutine.rs

@@ -3,6 +3,7 @@ use crate::{
     coroutine::{Coro, Variant},
     frame::FrameRef,
     function::OptionalArg,
+    protocol::PyIterReturn,
     slots::{IteratorIterable, SlotIterator},
     IdProtocol, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue, VirtualMachine,
 };
@@ -103,8 +104,9 @@ impl PyCoroutine {
 
 impl IteratorIterable for PyCoroutine {}
 impl SlotIterator for PyCoroutine {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        zelf.send(vm.ctx.none(), vm)
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+        // TODO: Fix zelf.send to return PyIterReturn
+        PyIterReturn::from_result(zelf.send(vm.ctx.none(), vm), vm)
     }
 }
 
@@ -141,8 +143,9 @@ impl PyCoroutineWrapper {
 
 impl IteratorIterable for PyCoroutineWrapper {}
 impl SlotIterator for PyCoroutineWrapper {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        zelf.send(vm.ctx.none(), vm)
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+        // TODO: Fix zelf.send to return PyIterReturn
+        PyIterReturn::from_result(zelf.send(vm.ctx.none(), vm), vm)
     }
 }
 

vm/src/builtins/dict.rs

@@ -4,7 +4,7 @@ use crate::{
     common::ascii,
     dictdatatype::{self, DictKey},
     function::{ArgIterable, FuncArgs, KwArgs, OptionalArg},
-    iterator,
+    protocol::PyIterReturn,
     slots::{
         Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotIterator, Unhashable,
     },
@@ -86,7 +86,7 @@ impl PyDict {
                 }
             } else if let Some(keys) = vm.get_method(dict_obj.clone(), "keys") {
                 let keys = vm.invoke(&keys?, ())?.get_iter(vm)?;
-                while let Some(key) = iterator::get_next_object(vm, &keys)? {
+                while let PyIterReturn::Return(key) = keys.next(vm)? {
                     let val = dict_obj.get_item(key.clone(), vm)?;
                     dict.insert(vm, key, val)?;
                 }
@@ -96,15 +96,20 @@ impl PyDict {
                     fn err(vm: &VirtualMachine) -> PyBaseExceptionRef {
                         vm.new_value_error("Iterator must have exactly two elements".to_owned())
                     }
-                    let element = match iterator::get_next_object(vm, &iter)? {
-                        Some(obj) => obj,
-                        None => break,
+                    let element = match iter.next(vm)? {
+                        PyIterReturn::Return(obj) => obj,
+                        PyIterReturn::StopIteration(_) => break,
                     };
                     let elem_iter = element.get_iter(vm)?;
-                    let key = iterator::get_next_object(vm, &elem_iter)?.ok_or_else(|| err(vm))?;
-                    let value =
-                        iterator::get_next_object(vm, &elem_iter)?.ok_or_else(|| err(vm))?;
-                    if iterator::get_next_object(vm, &elem_iter)?.is_some() {
+                    let key = match elem_iter.next(vm)? {
+                        PyIterReturn::Return(obj) => obj,
+                        PyIterReturn::StopIteration(_) => return Err(err(vm)),
+                    };
+                    let value = match elem_iter.next(vm)? {
+                        PyIterReturn::Return(obj) => obj,
+                        PyIterReturn::StopIteration(_) => return Err(err(vm)),
+                    };
+                    if matches!(elem_iter.next(vm)?, PyIterReturn::Return(_)) {
                         return Err(err(vm));
                     }
                     dict.insert(vm, key, value)?;
@@ -734,9 +739,9 @@ macro_rules! dict_iterator {
         impl IteratorIterable for $iter_name {}
         impl SlotIterator for $iter_name {
             #[allow(clippy::redundant_closure_call)]
-            fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+            fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
                 match zelf.status.load() {
-                    IterStatus::Exhausted => Err(vm.new_stop_iteration()),
+                    IterStatus::Exhausted => Ok(PyIterReturn::StopIteration(None)),
                     IterStatus::Active => {
                         if zelf.dict.entries.has_changed_size(&zelf.size) {
                             zelf.status.store(IterStatus::Exhausted);
@@ -745,10 +750,12 @@ macro_rules! dict_iterator {
                             ));
                         }
                         match zelf.dict.entries.next_entry_atomic(&zelf.position) {
-                            Some((key, value)) => Ok(($result_fn)(vm, key, value)),
+                            Some((key, value)) => {
+                                Ok(PyIterReturn::Return(($result_fn)(vm, key, value)))
+                            }
                             None => {
                                 zelf.status.store(IterStatus::Exhausted);
-                                Err(vm.new_stop_iteration())
+                                Ok(PyIterReturn::StopIteration(None))
                             }
                         }
                     }
@@ -795,9 +802,9 @@ macro_rules! dict_iterator {
         impl IteratorIterable for $reverse_iter_name {}
         impl SlotIterator for $reverse_iter_name {
             #[allow(clippy::redundant_closure_call)]
-            fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+            fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
                 match zelf.status.load() {
-                    IterStatus::Exhausted => Err(vm.new_stop_iteration()),
+                    IterStatus::Exhausted => Ok(PyIterReturn::StopIteration(None)),
                     IterStatus::Active => {
                         if zelf.dict.entries.has_changed_size(&zelf.size) {
                             zelf.status.store(IterStatus::Exhausted);
@@ -806,10 +813,12 @@ macro_rules! dict_iterator {
                             ));
                         }
                         match zelf.dict.entries.next_entry_atomic_reversed(&zelf.position) {
-                            Some((key, value)) => Ok(($result_fn)(vm, key, value)),
+                            Some((key, value)) => {
+                                Ok(PyIterReturn::Return(($result_fn)(vm, key, value)))
+                            }
                             None => {
                                 zelf.status.store(IterStatus::Exhausted);
-                                Err(vm.new_stop_iteration())
+                                Ok(PyIterReturn::StopIteration(None))
                             }
                         }
                     }

vm/src/builtins/enumerate.rs

@@ -6,7 +6,7 @@ use super::{
 use crate::common::lock::PyRwLock;
 use crate::{
     function::OptionalArg,
-    protocol::PyIter,
+    protocol::{PyIter, PyIterReturn},
     slots::{IteratorIterable, SlotConstructor, SlotIterator},
     IntoPyObject, ItemProtocol, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue,
     TypeProtocol, VirtualMachine,
@@ -57,12 +57,15 @@ impl PyEnumerate {}
 
 impl IteratorIterable for PyEnumerate {}
 impl SlotIterator for PyEnumerate {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        let next_obj = zelf.iterator.next(vm)?;
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+        let next_obj = match zelf.iterator.next(vm)? {
+            PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            PyIterReturn::Return(obj) => obj,
+        };
         let mut counter = zelf.counter.write();
         let position = counter.clone();
         *counter += 1;
-        Ok((position, next_obj).into_pyobject(vm))
+        Ok(PyIterReturn::Return((position, next_obj).into_pyobject(vm)))
     }
 }
 
@@ -139,21 +142,23 @@ impl PyReverseSequenceIterator {
 
 impl IteratorIterable for PyReverseSequenceIterator {}
 impl SlotIterator for PyReverseSequenceIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         if let Exhausted = zelf.status.load() {
-            return Err(vm.new_stop_iteration());
+            return Ok(PyIterReturn::StopIteration(None));
         }
         let pos = zelf.position.fetch_sub(1);
         if pos == 0 {
             zelf.status.store(Exhausted);
         }
         match zelf.obj.get_item(pos, vm) {
-            Err(ref e) if e.isinstance(&vm.ctx.exceptions.index_error) => {
+            Err(ref e)
+                if e.isinstance(&vm.ctx.exceptions.index_error)
+                    || e.isinstance(&vm.ctx.exceptions.stop_iteration) =>
+            {
                 zelf.status.store(Exhausted);
-                Err(vm.new_stop_iteration())
+                Ok(PyIterReturn::StopIteration(None))
             }
-            // also catches stop_iteration => stop_iteration
-            ret => ret,
+            other => other.map(PyIterReturn::Return),
         }
     }
 }

vm/src/builtins/filter.rs

@@ -1,6 +1,6 @@
 use super::PyTypeRef;
 use crate::{
-    protocol::PyIter,
+    protocol::{PyIter, PyIterReturn},
     slots::{IteratorIterable, SlotConstructor, SlotIterator},
     PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue, VirtualMachine,
 };
@@ -39,19 +39,25 @@ impl PyFilter {}
 
 impl IteratorIterable for PyFilter {}
 impl SlotIterator for PyFilter {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         let predicate = &zelf.predicate;
         loop {
-            let next_obj = zelf.iterator.next(vm)?;
+            let next_obj = match zelf.iterator.next(vm)? {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            };
             let predicate_value = if vm.is_none(predicate) {
                 next_obj.clone()
             } else {
                 // the predicate itself can raise StopIteration which does stop the filter
                 // iteration
-                vm.invoke(predicate, vec![next_obj.clone()])?
+                match PyIterReturn::from_result(vm.invoke(predicate, vec![next_obj.clone()]), vm)? {
+                    PyIterReturn::Return(obj) => obj,
+                    PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+                }
             };
             if predicate_value.try_to_bool(vm)? {
-                return Ok(next_obj);
+                return Ok(PyIterReturn::Return(next_obj));
             }
         }
     }

vm/src/builtins/generator.rs

@@ -7,6 +7,7 @@ use crate::{
     coroutine::{Coro, Variant},
     frame::FrameRef,
     function::OptionalArg,
+    protocol::PyIterReturn,
     slots::{IteratorIterable, SlotIterator},
     IdProtocol, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue, VirtualMachine,
 };
@@ -96,8 +97,9 @@ impl PyGenerator {
 
 impl IteratorIterable for PyGenerator {}
 impl SlotIterator for PyGenerator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        zelf.send(vm.ctx.none(), vm)
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+        // TODO: Fix zelf.send to return PyIterReturn
+        PyIterReturn::from_result(zelf.send(vm.ctx.none(), vm), vm)
     }
 }
 

vm/src/builtins/iter.rs

@@ -5,6 +5,7 @@
 use super::{int, PyInt, PyTypeRef};
 use crate::{
     function::ArgCallable,
+    protocol::PyIterReturn,
     slots::{IteratorIterable, SlotIterator},
     ItemProtocol, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue, TypeProtocol,
     VirtualMachine,
@@ -92,18 +93,20 @@ impl PySequenceIterator {
 
 impl IteratorIterable for PySequenceIterator {}
 impl SlotIterator for PySequenceIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         if let IterStatus::Exhausted = zelf.status.load() {
-            return Err(vm.new_stop_iteration());
+            return Ok(PyIterReturn::StopIteration(None));
         }
         let pos = zelf.position.fetch_add(1);
         match zelf.obj.get_item(pos, vm) {
-            Err(ref e) if e.isinstance(&vm.ctx.exceptions.index_error) => {
+            Err(ref e)
+                if e.isinstance(&vm.ctx.exceptions.index_error)
+                    || e.isinstance(&vm.ctx.exceptions.stop_iteration) =>
+            {
                 zelf.status.store(IterStatus::Exhausted);
-                Err(vm.new_stop_iteration())
+                Ok(PyIterReturn::StopIteration(None))
             }
-            // also catches stop_iteration => stop_iteration
-            ret => ret,
+            ret => ret.map(PyIterReturn::Return),
         }
     }
 }
@@ -135,16 +138,16 @@ impl PyCallableIterator {
 
 impl IteratorIterable for PyCallableIterator {}
 impl SlotIterator for PyCallableIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         if let IterStatus::Exhausted = zelf.status.load() {
-            return Err(vm.new_stop_iteration());
+            return Ok(PyIterReturn::StopIteration(None));
         }
         let ret = zelf.callable.invoke((), vm)?;
         if vm.bool_eq(&ret, &zelf.sentinel)? {
             zelf.status.store(IterStatus::Exhausted);
-            Err(vm.new_stop_iteration())
+            Ok(PyIterReturn::StopIteration(None))
         } else {
-            Ok(ret)
+            Ok(PyIterReturn::Return(ret))
         }
     }
 }

vm/src/builtins/list.rs

@@ -8,6 +8,7 @@ use crate::common::lock::{
 };
 use crate::{
     function::{ArgIterable, FuncArgs, OptionalArg},
+    protocol::PyIterReturn,
     sequence::{self, SimpleSeq},
     sliceable::{PySliceableSequence, PySliceableSequenceMut, SequenceIndex},
     slots::{
@@ -524,17 +525,17 @@ impl PyListIterator {
 
 impl IteratorIterable for PyListIterator {}
 impl SlotIterator for PyListIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         if let Exhausted = zelf.status.load() {
-            return Err(vm.new_stop_iteration());
+            return Ok(PyIterReturn::StopIteration(None));
         }
         let list = zelf.list.borrow_vec();
         let pos = zelf.position.fetch_add(1);
         if let Some(obj) = list.get(pos) {
-            Ok(obj.clone())
+            Ok(PyIterReturn::Return(obj.clone()))
         } else {
             zelf.status.store(Exhausted);
-            Err(vm.new_stop_iteration())
+            Ok(PyIterReturn::StopIteration(None))
         }
     }
 }
@@ -598,15 +599,15 @@ impl PyListReverseIterator {
 
 impl IteratorIterable for PyListReverseIterator {}
 impl SlotIterator for PyListReverseIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         if let Exhausted = zelf.status.load() {
-            return Err(vm.new_stop_iteration());
+            return Ok(PyIterReturn::StopIteration(None));
         }
         let list = zelf.list.borrow_vec();
         let pos = zelf.position.fetch_sub(1);
         if pos > 0 {
             if let Some(obj) = list.get(pos) {
-                return Ok(obj.clone());
+                return Ok(PyIterReturn::Return(obj.clone()));
             }
         }
         // We either are == 0 or list.get returned None. Either way, set status
@@ -614,10 +615,10 @@ impl SlotIterator for PyListReverseIterator {
         zelf.status.store(Exhausted);
         if pos == 0 {
             if let Some(obj) = list.get(pos) {
-                return Ok(obj.clone());
+                return Ok(PyIterReturn::Return(obj.clone()));
             }
         }
-        Err(vm.new_stop_iteration())
+        Ok(PyIterReturn::StopIteration(None))
     }
 }
 

vm/src/builtins/map.rs

@@ -2,7 +2,7 @@ use super::PyTypeRef;
 use crate::{
     function::PosArgs,
     iterator,
-    protocol::PyIter,
+    protocol::{PyIter, PyIterReturn},
     slots::{IteratorIterable, SlotConstructor, SlotIterator},
     PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue, VirtualMachine,
 };
@@ -47,15 +47,18 @@ impl PyMap {
 
 impl IteratorIterable for PyMap {}
 impl SlotIterator for PyMap {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        let next_objs = zelf
-            .iterators
-            .iter()
-            .map(|iterator| iterator.next(vm))
-            .collect::<Result<Vec<_>, _>>()?;
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+        let mut next_objs = Vec::new();
+        for iterator in zelf.iterators.iter() {
+            let item = match iterator.next(vm)? {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            };
+            next_objs.push(item);
+        }
 
         // the mapper itself can raise StopIteration which does stop the map iteration
-        vm.invoke(&zelf.mapper, next_objs)
+        PyIterReturn::from_result(vm.invoke(&zelf.mapper, next_objs), vm)
     }
 }
 

vm/src/builtins/pystr.rs

@@ -8,6 +8,7 @@ use crate::{
     exceptions::IntoPyException,
     format::{FormatSpec, FormatString, FromTemplate},
     function::{ArgIterable, FuncArgs, OptionalArg, OptionalOption},
+    protocol::PyIterReturn,
     sliceable::PySliceableSequence,
     slots::{
         Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotConstructor,
@@ -230,21 +231,24 @@ impl PyStrIterator {
 
 impl IteratorIterable for PyStrIterator {}
 impl SlotIterator for PyStrIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         if let Exhausted = zelf.status.load() {
-            return Err(vm.new_stop_iteration());
+            return Ok(PyIterReturn::StopIteration(None));
         }
         let value = &*zelf.string.as_str();
         let mut start = zelf.position.load(atomic::Ordering::SeqCst);
         loop {
             if start == value.len() {
                 zelf.status.store(Exhausted);
-                return Err(vm.new_stop_iteration());
+                return Ok(PyIterReturn::StopIteration(None));
             }
-            let ch = value[start..].chars().next().ok_or_else(|| {
-                zelf.status.store(Exhausted);
-                vm.new_stop_iteration()
-            })?;
+            let ch = match value[start..].chars().next() {
+                Some(ch) => ch,
+                None => {
+                    zelf.status.store(Exhausted);
+                    return Ok(PyIterReturn::StopIteration(None));
+                }
+            };
 
             match zelf.position.compare_exchange_weak(
                 start,
@@ -252,7 +256,7 @@ impl SlotIterator for PyStrIterator {
                 atomic::Ordering::Release,
                 atomic::Ordering::Relaxed,
             ) {
-                Ok(_) => break Ok(ch.into_pyobject(vm)),
+                Ok(_) => break Ok(PyIterReturn::Return(ch.into_pyobject(vm))),
                 Err(cur) => start = cur,
             }
         }

vm/src/builtins/pytype.rs

@@ -5,6 +5,7 @@ use super::{
 use crate::common::{ascii, lock::PyRwLock};
 use crate::{
     function::{FuncArgs, KwArgs, OptionalArg},
+    protocol::PyIterReturn,
     slots::{self, Callable, PyTypeFlags, PyTypeSlots, SlotGetattro, SlotSetattro},
     utils::Either,
     IdProtocol, PyAttributes, PyClassImpl, PyContext, PyLease, PyObjectRef, PyRef, PyResult,
@@ -261,8 +262,12 @@ impl PyType {
                 update_slot!(iter, func);
             }
             "__next__" => {
-                let func: slots::IterNextFunc =
-                    |zelf, vm| vm.call_special_method(zelf.clone(), "__next__", ());
+                let func: slots::IterNextFunc = |zelf, vm| {
+                    PyIterReturn::from_result(
+                        vm.call_special_method(zelf.clone(), "__next__", ()),
+                        vm,
+                    )
+                };
                 update_slot!(iternext, func);
             }
             _ => {}

vm/src/builtins/range.rs

@@ -2,7 +2,7 @@ use super::{PyInt, PyIntRef, PySlice, PySliceRef, PyTypeRef};
 use crate::common::hash::PyHash;
 use crate::{
     function::{FuncArgs, OptionalArg},
-    iterator,
+    protocol::PyIterReturn,
     slots::{Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotIterator},
     IdProtocol, IntoPyRef, PyClassImpl, PyContext, PyObjectRef, PyRef, PyResult, PyValue,
     TryFromObject, TypeProtocol, VirtualMachine,
@@ -31,7 +31,7 @@ fn iter_search(
 ) -> PyResult<usize> {
     let mut count = 0;
     let iter = obj.get_iter(vm)?;
-    while let Some(element) = iterator::get_next_object(vm, &iter)? {
+    while let PyIterReturn::Return(element) = iter.next(vm)? {
         if vm.bool_eq(&item, &element)? {
             match flag {
                 SearchType::Index => return Ok(count),
@@ -515,17 +515,18 @@ impl PyLongRangeIterator {
 
 impl IteratorIterable for PyLongRangeIterator {}
 impl SlotIterator for PyLongRangeIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         // TODO: In pathological case (index == usize::MAX) this can wrap around
         // (since fetch_add wraps). This would result in the iterator spinning again
         // from the beginning.
         let index = BigInt::from(zelf.index.fetch_add(1));
         if index < zelf.length {
-            Ok(vm
-                .ctx
-                .new_int(zelf.start.clone() + index * zelf.step.clone()))
+            Ok(PyIterReturn::Return(
+                vm.ctx
+                    .new_int(zelf.start.clone() + index * zelf.step.clone()),
+            ))
         } else {
-            Err(vm.new_stop_iteration())
+            Ok(PyIterReturn::StopIteration(None))
         }
     }
 }
@@ -585,15 +586,17 @@ impl PyRangeIterator {
 
 impl IteratorIterable for PyRangeIterator {}
 impl SlotIterator for PyRangeIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         // TODO: In pathological case (index == usize::MAX) this can wrap around
         // (since fetch_add wraps). This would result in the iterator spinning again
         // from the beginning.
         let index = zelf.index.fetch_add(1);
         if index < zelf.length {
-            Ok(vm.ctx.new_int(zelf.start + (index as isize) * zelf.step))
+            Ok(PyIterReturn::Return(
+                vm.ctx.new_int(zelf.start + (index as isize) * zelf.step),
+            ))
         } else {
-            Err(vm.new_stop_iteration())
+            Ok(PyIterReturn::StopIteration(None))
         }
     }
 }

vm/src/builtins/set.rs

@@ -6,6 +6,7 @@ use crate::common::{ascii, hash::PyHash, rc::PyRc};
 use crate::{
     dictdatatype::{self, DictSize},
     function::{ArgIterable, FuncArgs, OptionalArg, PosArgs},
+    protocol::PyIterReturn,
     slots::{
         Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotConstructor,
         SlotIterator, Unhashable,
@@ -863,9 +864,9 @@ impl PySetIterator {
 
 impl IteratorIterable for PySetIterator {}
 impl SlotIterator for PySetIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         match zelf.status.load() {
-            IterStatus::Exhausted => Err(vm.new_stop_iteration()),
+            IterStatus::Exhausted => Ok(PyIterReturn::StopIteration(None)),
             IterStatus::Active => {
                 if zelf.dict.has_changed_size(&zelf.size) {
                     zelf.status.store(IterStatus::Exhausted);
@@ -874,10 +875,10 @@ impl SlotIterator for PySetIterator {
                     );
                 }
                 match zelf.dict.next_entry_atomic(&zelf.position) {
-                    Some((key, _)) => Ok(key),
+                    Some((key, _)) => Ok(PyIterReturn::Return(key)),
                     None => {
                         zelf.status.store(IterStatus::Exhausted);
-                        Err(vm.new_stop_iteration())
+                        Ok(PyIterReturn::StopIteration(None))
                     }
                 }
             }

vm/src/builtins/tuple.rs

@@ -6,6 +6,7 @@ use super::{
 use crate::common::hash::PyHash;
 use crate::{
     function::OptionalArg,
+    protocol::PyIterReturn,
     sequence::{self, SimpleSeq},
     sliceable::PySliceableSequence,
     slots::{
@@ -378,16 +379,16 @@ impl PyTupleIterator {
 
 impl IteratorIterable for PyTupleIterator {}
 impl SlotIterator for PyTupleIterator {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         if let Exhausted = zelf.status.load() {
-            return Err(vm.new_stop_iteration());
+            return Ok(PyIterReturn::StopIteration(None));
         }
         let pos = zelf.position.fetch_add(1);
         if let Some(obj) = zelf.tuple.as_slice().get(pos) {
-            Ok(obj.clone())
+            Ok(PyIterReturn::Return(obj.clone()))
         } else {
             zelf.status.store(Exhausted);
-            Err(vm.new_stop_iteration())
+            Ok(PyIterReturn::StopIteration(None))
         }
     }
 }

vm/src/builtins/zip.rs

@@ -1,7 +1,7 @@
 use super::PyTypeRef;
 use crate::{
     function::PosArgs,
-    protocol::PyIter,
+    protocol::{PyIter, PyIterReturn},
     slots::{IteratorIterable, SlotConstructor, SlotIterator},
     PyClassImpl, PyContext, PyRef, PyResult, PyValue, VirtualMachine,
 };
@@ -32,18 +32,19 @@ impl PyZip {}
 
 impl IteratorIterable for PyZip {}
 impl SlotIterator for PyZip {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         if zelf.iterators.is_empty() {
-            Err(vm.new_stop_iteration())
-        } else {
-            let next_objs = zelf
-                .iterators
-                .iter()
-                .map(|iterator| iterator.next(vm))
-                .collect::<Result<Vec<_>, _>>()?;
-
-            Ok(vm.ctx.new_tuple(next_objs))
+            return Ok(PyIterReturn::StopIteration(None));
         }
+        let mut next_objs = Vec::new();
+        for iterator in zelf.iterators.iter() {
+            let item = match iterator.next(vm)? {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            };
+            next_objs.push(item);
+        }
+        Ok(PyIterReturn::Return(vm.ctx.new_tuple(next_objs)))
     }
 }
 

vm/src/frame.rs

@@ -15,12 +15,12 @@ use crate::{
     exceptions::{self, ExceptionCtor},
     function::FuncArgs,
     iterator,
-    protocol::PyIter,
+    protocol::{PyIter, PyIterReturn},
     scope::Scope,
     slots::PyComparisonOp,
     stdlib::builtins,
-    IdProtocol, ItemProtocol, PyMethod, PyObjectRef, PyRef, PyResult, PyValue, TryFromObject,
-    TypeProtocol, VirtualMachine,
+    IdProtocol, IntoPyResult, ItemProtocol, PyMethod, PyObjectRef, PyRef, PyResult, PyValue,
+    TryFromObject, TypeProtocol, VirtualMachine,
 };
 use indexmap::IndexMap;
 use itertools::Itertools;
@@ -1442,7 +1442,8 @@ impl ExecutingFrame<'_> {
     fn _send(&self, coro: &PyObjectRef, val: PyObjectRef, vm: &VirtualMachine) -> PyResult {
         match self.builtin_coro(coro) {
             Some(coro) => coro.send(val, vm),
-            None if vm.is_none(&val) => PyIter::new(coro).next(vm),
+            // FIXME: turn return type to PyResult<PyIterReturn> then ExecutionResult will be simplified
+            None if vm.is_none(&val) => PyIter::new(coro).next(vm).into_pyresult(vm),
             None => {
                 let meth = vm.get_attribute(coro.clone(), "send")?;
                 vm.invoke(&meth, (val,))
@@ -1513,15 +1514,15 @@ impl ExecutingFrame<'_> {
     /// The top of stack contains the iterator, lets push it forward
     fn execute_for_iter(&mut self, vm: &VirtualMachine, target: bytecode::Label) -> FrameResult {
         let top_of_stack = PyIter::new(self.last_value());
-        let next_obj = iterator::get_next_object(vm, &top_of_stack);
+        let next_obj = top_of_stack.next(vm);
 
         // Check the next object:
         match next_obj {
-            Ok(Some(value)) => {
+            Ok(PyIterReturn::Return(value)) => {
                 self.push_value(value);
                 Ok(None)
             }
-            Ok(None) => {
+            Ok(PyIterReturn::StopIteration(_)) => {
                 // Pop iterator from stack:
                 self.pop_value();
 

vm/src/function/argument.rs

@@ -1,7 +1,9 @@
 use super::IntoFuncArgs;
 use crate::{
-    builtins::iter::PySequenceIterator, iterator, protocol::PyIter, PyObjectRef, PyResult, PyValue,
-    TryFromObject, TypeProtocol, VirtualMachine,
+    builtins::iter::PySequenceIterator,
+    iterator,
+    protocol::{PyIter, PyIterReturn},
+    PyObjectRef, PyResult, PyValue, TryFromObject, TypeProtocol, VirtualMachine,
 };
 use std::marker::PhantomData;
 
@@ -102,7 +104,12 @@ where
     type Item = PyResult<T>;
 
     fn next(&mut self) -> Option<Self::Item> {
-        iterator::get_next_object(self.vm, &PyIter::new(&self.obj))
+        PyIter::new(&self.obj)
+            .next(self.vm)
+            .map(|iret| match iret {
+                PyIterReturn::Return(obj) => Some(obj),
+                PyIterReturn::StopIteration(_) => None,
+            })
             .transpose()
             .map(|x| x.and_then(|obj| T::try_from_object(self.vm, obj)))
     }

vm/src/iterator.rs

@@ -4,36 +4,11 @@
 
 use crate::{
     builtins::{int, PyBaseExceptionRef, PyInt},
-    protocol::PyIter,
+    protocol::{PyIter, PyIterReturn},
     IdProtocol, PyObjectRef, PyResult, TypeProtocol, VirtualMachine,
 };
 use num_traits::Signed;
 
-/*
- * Helper function to retrieve the next object (or none) from an iterator.
- */
-pub fn get_next_object<T>(
-    vm: &VirtualMachine,
-    iter_obj: &PyIter<T>,
-) -> PyResult<Option<PyObjectRef>>
-where
-    T: std::borrow::Borrow<PyObjectRef>,
-{
-    let next_obj: PyResult = iter_obj.next(vm);
-
-    match next_obj {
-        Ok(value) => Ok(Some(value)),
-        Err(next_error) => {
-            // Check if we have stopiteration, or something else:
-            if next_error.isinstance(&vm.ctx.exceptions.stop_iteration) {
-                Ok(None)
-            } else {
-                Err(next_error)
-            }
-        }
-    }
-}
-
 pub fn try_map<F, R>(vm: &VirtualMachine, iter: &PyIter, cap: usize, mut f: F) -> PyResult<Vec<R>>
 where
     F: FnMut(PyObjectRef) -> PyResult<R>,
@@ -44,7 +19,7 @@ where
         return Ok(Vec::new());
     }
     let mut results = Vec::with_capacity(cap);
-    while let Some(element) = get_next_object(vm, iter)? {
+    while let PyIterReturn::Return(element) = iter.next(vm)? {
         results.push(f(element)?);
     }
     results.shrink_to_fit();

vm/src/protocol/iter.rs

@@ -1,7 +1,7 @@
 use crate::IntoPyObject;
 use crate::{
-    builtins::iter::PySequenceIterator, PyObjectRef, PyResult, PyValue, TryFromObject,
-    TypeProtocol, VirtualMachine,
+    builtins::iter::PySequenceIterator, IntoPyResult, PyObjectRef, PyResult, PyValue,
+    TryFromObject, TypeProtocol, VirtualMachine,
 };
 use std::borrow::Borrow;
 use std::ops::Deref;
@@ -35,7 +35,7 @@ where
     pub fn as_object(&self) -> &PyObjectRef {
         self.0.borrow()
     }
-    pub fn next(&self, vm: &VirtualMachine) -> PyResult {
+    pub fn next(&self, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         let iternext = {
             self.0
                 .borrow()
@@ -119,3 +119,39 @@ impl PyObjectRef {
         PyIter::try_from_object(vm, self)
     }
 }
+
+pub enum PyIterReturn<T = PyObjectRef> {
+    Return(T),
+    StopIteration(Option<PyObjectRef>),
+}
+
+impl PyIterReturn {
+    pub fn from_result(result: PyResult, vm: &VirtualMachine) -> PyResult<Self> {
+        match result {
+            Ok(obj) => Ok(Self::Return(obj)),
+            Err(err) if err.isinstance(&vm.ctx.exceptions.stop_iteration) => {
+                let args = err.get_arg(0);
+                Ok(Self::StopIteration(args))
+            }
+            Err(err) => Err(err),
+        }
+    }
+}
+
+impl IntoPyResult for PyIterReturn {
+    fn into_pyresult(self, vm: &VirtualMachine) -> PyResult {
+        match self {
+            Self::Return(obj) => Ok(obj),
+            Self::StopIteration(v) => Err({
+                let args = if let Some(v) = v { vec![v] } else { Vec::new() };
+                vm.new_exception(vm.ctx.exceptions.stop_iteration.clone(), args)
+            }),
+        }
+    }
+}
+
+impl IntoPyResult for PyResult<PyIterReturn> {
+    fn into_pyresult(self, vm: &VirtualMachine) -> PyResult {
+        self.and_then(|obj| obj.into_pyresult(vm))
+    }
+}

vm/src/protocol/mod.rs

@@ -2,4 +2,4 @@ mod buffer;
 mod iter;
 
 pub use buffer::{BufferInternal, BufferOptions, PyBuffer, ResizeGuard};
-pub use iter::PyIter;
+pub use iter::{PyIter, PyIterReturn};

vm/src/slots.rs

@@ -2,12 +2,12 @@ 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;
+use crate::protocol::{PyBuffer, PyIterReturn};
 use crate::utils::Either;
 use crate::VirtualMachine;
 use crate::{
-    IdProtocol, PyComparisonValue, PyObjectRef, PyRef, PyResult, PyValue, TryFromObject,
-    TypeProtocol,
+    IdProtocol, IntoPyResult, PyComparisonValue, PyObjectRef, PyRef, PyResult, PyValue,
+    TryFromObject, TypeProtocol,
 };
 use crossbeam_utils::atomic::AtomicCell;
 use std::cmp::Ordering;
@@ -71,7 +71,7 @@ pub(crate) type SetattroFunc =
     fn(&PyObjectRef, PyStrRef, Option<PyObjectRef>, &VirtualMachine) -> PyResult<()>;
 pub(crate) type BufferFunc = fn(&PyObjectRef, &VirtualMachine) -> PyResult<PyBuffer>;
 pub(crate) type IterFunc = fn(PyObjectRef, &VirtualMachine) -> PyResult;
-pub(crate) type IterNextFunc = 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
@@ -550,7 +550,7 @@ pub trait Iterable: PyValue {
 #[pyimpl(with(Iterable))]
 pub trait SlotIterator: PyValue + Iterable {
     #[pyslot]
-    fn slot_iternext(zelf: &PyObjectRef, vm: &VirtualMachine) -> PyResult {
+    fn slot_iternext(zelf: &PyObjectRef, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
         if let Some(zelf) = zelf.downcast_ref() {
             Self::next(zelf, vm)
         } else {
@@ -558,11 +558,11 @@ pub trait SlotIterator: PyValue + Iterable {
         }
     }
 
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult;
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn>;
 
     #[pymethod]
     fn __next__(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult {
-        Self::slot_iternext(&zelf, vm)
+        Self::slot_iternext(&zelf, vm).into_pyresult(vm)
     }
 }
 

vm/src/stdlib/builtins.rs

@@ -25,7 +25,7 @@ mod builtins {
             ArgBytesLike, ArgCallable, ArgIterable, FuncArgs, KwArgs, OptionalArg, OptionalOption,
             PosArgs,
         },
-        protocol::PyIter,
+        protocol::{PyIter, PyIterReturn},
         py_io,
         readline::{Readline, ReadlineResult},
         scope::Scope,
@@ -512,19 +512,17 @@ mod builtins {
         iterator: PyObjectRef,
         default_value: OptionalArg<PyObjectRef>,
         vm: &VirtualMachine,
-    ) -> PyResult {
+    ) -> PyResult<PyIterReturn> {
         if !PyIter::check(&iterator) {
             return Err(vm.new_type_error(format!(
                 "{} object is not an iterator",
                 iterator.class().name()
             )));
         }
-
-        PyIter::new(iterator).next(vm).or_else(|err| {
-            if err.isinstance(&vm.ctx.exceptions.stop_iteration) {
-                default_value.ok_or(err)
-            } else {
-                Err(err)
+        PyIter::new(iterator).next(vm).map(|iret| match iret {
+            PyIterReturn::Return(obj) => PyIterReturn::Return(obj),
+            PyIterReturn::StopIteration(v) => {
+                default_value.map_or(PyIterReturn::StopIteration(v), PyIterReturn::Return)
             }
         })
     }

vm/src/stdlib/collections.rs

@@ -9,6 +9,7 @@ mod _collections {
             PyInt, PyTypeRef,
         },
         function::{FuncArgs, KwArgs, OptionalArg},
+        protocol::PyIterReturn,
         sequence, sliceable,
         slots::{
             Comparable, Hashable, Iterable, IteratorIterable, PyComparisonOp, SlotConstructor,
@@ -642,9 +643,9 @@ mod _collections {
 
     impl IteratorIterable for PyDequeIterator {}
     impl SlotIterator for PyDequeIterator {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             match zelf.status.load() {
-                Exhausted => Err(vm.new_stop_iteration()),
+                Exhausted => Ok(PyIterReturn::StopIteration(None)),
                 Active => {
                     if zelf.length != zelf.deque.len() {
                         // Deque was changed while we iterated.
@@ -655,10 +656,10 @@ mod _collections {
                         let deque = zelf.deque.borrow_deque();
                         if pos < deque.len() {
                             let ret = deque[pos].clone();
-                            Ok(ret)
+                            Ok(PyIterReturn::Return(ret))
                         } else {
                             zelf.status.store(Exhausted);
-                            Err(vm.new_stop_iteration())
+                            Ok(PyIterReturn::StopIteration(None))
                         }
                     }
                 }
@@ -722,9 +723,9 @@ mod _collections {
 
     impl IteratorIterable for PyReverseDequeIterator {}
     impl SlotIterator for PyReverseDequeIterator {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             match zelf.status.load() {
-                Exhausted => Err(vm.new_stop_iteration()),
+                Exhausted => Ok(PyIterReturn::StopIteration(None)),
                 Active => {
                     // If length changes while we iterate, set to Exhausted and bail.
                     if zelf.length != zelf.deque.len() {
@@ -735,7 +736,7 @@ mod _collections {
                         let deque = zelf.deque.borrow_deque();
                         if pos > 0 {
                             if let Some(obj) = deque.get(pos) {
-                                return Ok(obj.clone());
+                                return Ok(PyIterReturn::Return(obj.clone()));
                             }
                         }
                         // We either are == 0 or deque.get returned None. Either way, set status
@@ -743,9 +744,9 @@ mod _collections {
                         zelf.status.store(Exhausted);
                         if pos == 0 {
                             // Can safely index directly.
-                            return Ok(deque[pos].clone());
+                            return Ok(PyIterReturn::Return(deque[pos].clone()));
                         }
-                        Err(vm.new_stop_iteration())
+                        Ok(PyIterReturn::StopIteration(None))
                     }
                 }
             }

vm/src/stdlib/functools.rs

@@ -3,9 +3,9 @@ pub(crate) use _functools::make_module;
 #[pymodule]
 mod _functools {
     use crate::function::OptionalArg;
-    use crate::protocol::PyIter;
+    use crate::protocol::{PyIter, PyIterReturn};
     use crate::vm::VirtualMachine;
-    use crate::{PyObjectRef, PyResult, TypeProtocol};
+    use crate::{PyObjectRef, PyResult};
 
     #[pyfunction]
     fn reduce(
@@ -17,22 +17,25 @@ mod _functools {
         let start_value = if let OptionalArg::Present(val) = start_value {
             val
         } else {
-            iterator.next(vm).map_err(|err| {
-                if err.isinstance(&vm.ctx.exceptions.stop_iteration) {
+            iterator.next(vm).and_then(|iret| match iret {
+                PyIterReturn::Return(obj) => Ok(obj),
+                PyIterReturn::StopIteration(_) => Err({
                     let exc_type = vm.ctx.exceptions.type_error.clone();
                     vm.new_exception_msg(
                         exc_type,
                         "reduce() of empty sequence with no initial value".to_owned(),
                     )
-                } else {
-                    err
-                }
+                }),
             })?
         };
 
         let mut accumulator = start_value;
 
         while let Ok(next_obj) = iterator.next(vm) {
+            let next_obj = match next_obj {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(_) => break,
+            };
             accumulator = vm.invoke(&function, vec![accumulator, next_obj])?
         }
 

vm/src/stdlib/io.rs

@@ -85,7 +85,7 @@ mod _io {
         function::{
             ArgBytesLike, ArgIterable, ArgMemoryBuffer, FuncArgs, OptionalArg, OptionalOption,
         },
-        protocol::{BufferInternal, BufferOptions, PyBuffer, ResizeGuard},
+        protocol::{BufferInternal, BufferOptions, PyBuffer, PyIterReturn, ResizeGuard},
         slots::{Iterable, SlotConstructor, SlotIterator},
         utils::Either,
         vm::{ReprGuard, VirtualMachine},
@@ -524,16 +524,16 @@ mod _io {
     }
 
     impl SlotIterator for _IOBase {
-        fn slot_iternext(zelf: &PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        fn slot_iternext(zelf: &PyObjectRef, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let line = vm.call_method(zelf, "readline", ())?;
-            if !line.clone().try_to_bool(vm)? {
-                Err(vm.new_stop_iteration())
+            Ok(if !line.clone().try_to_bool(vm)? {
+                PyIterReturn::StopIteration(None)
             } else {
-                Ok(line)
-            }
+                PyIterReturn::Return(line)
+            })
         }
 
-        fn next(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult {
+        fn next(_zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             unreachable!("slot_iternext is implemented")
         }
     }

vm/src/stdlib/itertools.rs

@@ -9,8 +9,7 @@ mod decl {
     use crate::{
         builtins::{int, PyInt, PyIntRef, PyTupleRef, PyTypeRef},
         function::{ArgCallable, FuncArgs, OptionalArg, OptionalOption, PosArgs},
-        iterator::get_next_object,
-        protocol::PyIter,
+        protocol::{PyIter, PyIterReturn},
         slots::{IteratorIterable, SlotConstructor, SlotIterator},
         IdProtocol, IntoPyObject, PyObjectRef, PyRef, PyResult, PyValue, PyWeakRef, TypeProtocol,
         VirtualMachine,
@@ -57,7 +56,7 @@ mod decl {
     }
     impl IteratorIterable for PyItertoolsChain {}
     impl SlotIterator for PyItertoolsChain {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             loop {
                 let pos = zelf.cur_idx.load();
                 if pos >= zelf.iterables.len() {
@@ -77,19 +76,18 @@ mod decl {
 
                 // We need to call "next" outside of the lock.
                 match cur_iter.next(vm) {
-                    Ok(ok) => return Ok(ok),
+                    Ok(PyIterReturn::Return(ok)) => return Ok(PyIterReturn::Return(ok)),
+                    Ok(PyIterReturn::StopIteration(_)) => {
+                        zelf.cur_idx.fetch_add(1);
+                        *zelf.cached_iter.write() = None;
+                    }
                     Err(err) => {
-                        if err.isinstance(&vm.ctx.exceptions.stop_iteration) {
-                            zelf.cur_idx.fetch_add(1);
-                            *zelf.cached_iter.write() = None;
-                        } else {
-                            return Err(err);
-                        }
+                        return Err(err);
                     }
                 }
             }
 
-            Err(vm.new_stop_iteration())
+            Ok(PyIterReturn::StopIteration(None))
         }
     }
 
@@ -126,9 +124,12 @@ mod decl {
 
     impl IteratorIterable for PyItertoolsCompress {}
     impl SlotIterator for PyItertoolsCompress {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             loop {
-                let sel_obj = zelf.selector.next(vm)?;
+                let sel_obj = match zelf.selector.next(vm)? {
+                    PyIterReturn::Return(obj) => obj,
+                    PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+                };
                 let verdict = sel_obj.clone().try_to_bool(vm)?;
                 let data_obj = zelf.data.next(vm)?;
 
@@ -185,11 +186,11 @@ mod decl {
     impl PyItertoolsCount {}
     impl IteratorIterable for PyItertoolsCount {}
     impl SlotIterator for PyItertoolsCount {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let mut cur = zelf.cur.write();
             let result = cur.clone();
             *cur += &zelf.step;
-            Ok(result.into_pyobject(vm))
+            Ok(PyIterReturn::Return(result.into_pyobject(vm)))
         }
     }
 
@@ -219,14 +220,14 @@ mod decl {
     impl PyItertoolsCycle {}
     impl IteratorIterable for PyItertoolsCycle {}
     impl SlotIterator for PyItertoolsCycle {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-            let item = if let Some(item) = get_next_object(vm, &zelf.iter)? {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+            let item = if let PyIterReturn::Return(item) = zelf.iter.next(vm)? {
                 zelf.saved.write().push(item.clone());
                 item
             } else {
                 let saved = zelf.saved.read();
                 if saved.len() == 0 {
-                    return Err(vm.new_stop_iteration());
+                    return Ok(PyIterReturn::StopIteration(None));
                 }
 
                 let last_index = zelf.index.fetch_add(1);
@@ -238,7 +239,7 @@ mod decl {
                 saved[last_index].clone()
             };
 
-            Ok(item)
+            Ok(PyIterReturn::Return(item))
         }
     }
 
@@ -320,15 +321,15 @@ mod decl {
 
     impl IteratorIterable for PyItertoolsRepeat {}
     impl SlotIterator for PyItertoolsRepeat {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, _vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             if let Some(ref times) = zelf.times {
                 let mut times = times.write();
                 if *times == 0 {
-                    return Err(vm.new_stop_iteration());
+                    return Ok(PyIterReturn::StopIteration(None));
                 }
                 *times -= 1;
             }
-            Ok(zelf.object.clone())
+            Ok(PyIterReturn::Return(zelf.object.clone()))
         }
     }
 
@@ -365,11 +366,15 @@ mod decl {
     impl PyItertoolsStarmap {}
     impl IteratorIterable for PyItertoolsStarmap {}
     impl SlotIterator for PyItertoolsStarmap {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let obj = zelf.iter.next(vm)?;
             let function = &zelf.function;
-
-            vm.invoke(function, vm.extract_elements(&obj)?)
+            match obj {
+                PyIterReturn::Return(obj) => {
+                    PyIterReturn::from_result(vm.invoke(function, vm.extract_elements(&obj)?), vm)
+                }
+                PyIterReturn::StopIteration(v) => Ok(PyIterReturn::StopIteration(v)),
+            }
         }
     }
 
@@ -414,22 +419,25 @@ mod decl {
     impl PyItertoolsTakewhile {}
     impl IteratorIterable for PyItertoolsTakewhile {}
     impl SlotIterator for PyItertoolsTakewhile {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             if zelf.stop_flag.load() {
-                return Err(vm.new_stop_iteration());
+                return Ok(PyIterReturn::StopIteration(None));
             }
 
             // might be StopIteration or anything else, which is propagated upwards
-            let obj = zelf.iterable.next(vm)?;
+            let obj = match zelf.iterable.next(vm)? {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            };
             let predicate = &zelf.predicate;
 
             let verdict = vm.invoke(predicate, (obj.clone(),))?;
             let verdict = verdict.try_to_bool(vm)?;
             if verdict {
-                Ok(obj)
+                Ok(PyIterReturn::Return(obj))
             } else {
                 zelf.stop_flag.store(true);
-                Err(vm.new_stop_iteration())
+                Ok(PyIterReturn::StopIteration(None))
             }
         }
     }
@@ -475,18 +483,23 @@ mod decl {
     impl PyItertoolsDropwhile {}
     impl IteratorIterable for PyItertoolsDropwhile {}
     impl SlotIterator for PyItertoolsDropwhile {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let predicate = &zelf.predicate;
             let iterable = &zelf.iterable;
 
             if !zelf.start_flag.load() {
                 loop {
-                    let obj = iterable.next(vm)?;
+                    let obj = match iterable.next(vm)? {
+                        PyIterReturn::Return(obj) => obj,
+                        PyIterReturn::StopIteration(v) => {
+                            return Ok(PyIterReturn::StopIteration(v))
+                        }
+                    };
                     let pred = predicate.clone();
                     let pred_value = vm.invoke(&pred.into_object(), (obj.clone(),))?;
                     if !pred_value.try_to_bool(vm)? {
                         zelf.start_flag.store(true);
-                        return Ok(obj);
+                        return Ok(PyIterReturn::Return(obj));
                     }
                 }
             }
@@ -570,19 +583,25 @@ mod decl {
 
     #[pyimpl(with(SlotIterator, SlotConstructor))]
     impl PyItertoolsGroupBy {
-        pub(super) fn advance(&self, vm: &VirtualMachine) -> PyResult<(PyObjectRef, PyObjectRef)> {
-            let new_value = self.iterable.next(vm)?;
+        pub(super) fn advance(
+            &self,
+            vm: &VirtualMachine,
+        ) -> PyResult<PyIterReturn<(PyObjectRef, PyObjectRef)>> {
+            let new_value = match self.iterable.next(vm)? {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            };
             let new_key = if let Some(ref kf) = self.key_func {
                 vm.invoke(kf, vec![new_value.clone()])?
             } else {
                 new_value.clone()
             };
-            Ok((new_value, new_key))
+            Ok(PyIterReturn::Return((new_value, new_key)))
         }
     }
     impl IteratorIterable for PyItertoolsGroupBy {}
     impl SlotIterator for PyItertoolsGroupBy {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let mut state = zelf.state.lock();
             state.grouper = None;
 
@@ -593,13 +612,23 @@ mod decl {
 
                 let (value, key) = if let Some(old_key) = current_key {
                     loop {
-                        let (value, new_key) = zelf.advance(vm)?;
+                        let (value, new_key) = match zelf.advance(vm)? {
+                            PyIterReturn::Return(obj) => obj,
+                            PyIterReturn::StopIteration(v) => {
+                                return Ok(PyIterReturn::StopIteration(v))
+                            }
+                        };
                         if !vm.bool_eq(&new_key, &old_key)? {
                             break (value, new_key);
                         }
                     }
                 } else {
-                    zelf.advance(vm)?
+                    match zelf.advance(vm)? {
+                        PyIterReturn::Return(obj) => obj,
+                        PyIterReturn::StopIteration(v) => {
+                            return Ok(PyIterReturn::StopIteration(v))
+                        }
+                    }
                 };
 
                 state = zelf.state.lock();
@@ -615,7 +644,9 @@ mod decl {
             .into_ref(vm);
 
             state.grouper = Some(PyRef::downgrade(&grouper));
-            Ok((state.current_key.as_ref().unwrap().clone(), grouper).into_pyobject(vm))
+            Ok(PyIterReturn::Return(
+                (state.current_key.as_ref().unwrap().clone(), grouper).into_pyobject(vm),
+            ))
         }
     }
 
@@ -632,31 +663,34 @@ mod decl {
     impl PyItertoolsGrouper {}
     impl IteratorIterable for PyItertoolsGrouper {}
     impl SlotIterator for PyItertoolsGrouper {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let old_key = {
                 let mut state = zelf.groupby.state.lock();
 
                 if !state.is_current(zelf) {
-                    return Err(vm.new_stop_iteration());
+                    return Ok(PyIterReturn::StopIteration(None));
                 }
 
                 // check to see if the value has already been retrieved from the iterator
                 if let Some(val) = state.current_value.take() {
-                    return Ok(val);
+                    return Ok(PyIterReturn::Return(val));
                 }
 
                 state.current_key.as_ref().unwrap().clone()
             };
-            let (value, key) = zelf.groupby.advance(vm)?;
+            let (value, key) = match zelf.groupby.advance(vm)? {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            };
             if vm.bool_eq(&key, &old_key)? {
-                Ok(value)
+                Ok(PyIterReturn::Return(value))
             } else {
                 let mut state = zelf.groupby.state.lock();
                 state.current_value = Some(value);
                 state.current_key = Some(key);
                 state.next_group = true;
                 state.grouper = None;
-                Err(vm.new_stop_iteration())
+                Ok(PyIterReturn::StopIteration(None))
             }
         }
     }
@@ -762,7 +796,7 @@ mod decl {
 
     impl IteratorIterable for PyItertoolsIslice {}
     impl SlotIterator for PyItertoolsIslice {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             while zelf.cur.load() < zelf.next.load() {
                 zelf.iterable.next(vm)?;
                 zelf.cur.fetch_add(1);
@@ -770,18 +804,21 @@ mod decl {
 
             if let Some(stop) = zelf.stop {
                 if zelf.cur.load() >= stop {
-                    return Err(vm.new_stop_iteration());
+                    return Ok(PyIterReturn::StopIteration(None));
                 }
             }
 
-            let obj = zelf.iterable.next(vm)?;
+            let obj = match zelf.iterable.next(vm)? {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            };
             zelf.cur.fetch_add(1);
 
             // TODO is this overflow check required? attempts to copy CPython.
             let (next, ovf) = zelf.next.load().overflowing_add(zelf.step);
             zelf.next.store(if ovf { zelf.stop.unwrap() } else { next });
 
-            Ok(obj)
+            Ok(PyIterReturn::Return(obj))
         }
     }
 
@@ -824,12 +861,15 @@ mod decl {
     impl PyItertoolsFilterFalse {}
     impl IteratorIterable for PyItertoolsFilterFalse {}
     impl SlotIterator for PyItertoolsFilterFalse {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let predicate = &zelf.predicate;
             let iterable = &zelf.iterable;
 
             loop {
-                let obj = iterable.next(vm)?;
+                let obj = match iterable.next(vm)? {
+                    PyIterReturn::Return(obj) => obj,
+                    PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+                };
                 let pred_value = if vm.is_none(predicate) {
                     obj.clone()
                 } else {
@@ -837,7 +877,7 @@ mod decl {
                 };
 
                 if !pred_value.try_to_bool(vm)? {
-                    return Ok(obj);
+                    return Ok(PyIterReturn::Return(obj));
                 }
             }
         }
@@ -881,18 +921,28 @@ mod decl {
 
     impl IteratorIterable for PyItertoolsAccumulate {}
     impl SlotIterator for PyItertoolsAccumulate {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let iterable = &zelf.iterable;
 
             let acc_value = zelf.acc_value.read().clone();
 
             let next_acc_value = match acc_value {
                 None => match &zelf.initial {
-                    None => iterable.next(vm)?,
+                    None => match iterable.next(vm)? {
+                        PyIterReturn::Return(obj) => obj,
+                        PyIterReturn::StopIteration(v) => {
+                            return Ok(PyIterReturn::StopIteration(v))
+                        }
+                    },
                     Some(obj) => obj.clone(),
                 },
                 Some(value) => {
-                    let obj = iterable.next(vm)?;
+                    let obj = match iterable.next(vm)? {
+                        PyIterReturn::Return(obj) => obj,
+                        PyIterReturn::StopIteration(v) => {
+                            return Ok(PyIterReturn::StopIteration(v))
+                        }
+                    };
                     match &zelf.binop {
                         None => vm._add(&value, &obj)?,
                         Some(op) => vm.invoke(op, vec![value, obj])?,
@@ -901,7 +951,7 @@ mod decl {
             };
             *zelf.acc_value.write() = Some(next_acc_value.clone());
 
-            Ok(next_acc_value)
+            Ok(PyIterReturn::Return(next_acc_value))
         }
     }
 
@@ -919,12 +969,15 @@ mod decl {
             }))
         }
 
-        fn get_item(&self, vm: &VirtualMachine, index: usize) -> PyResult {
+        fn get_item(&self, vm: &VirtualMachine, index: usize) -> PyResult<PyIterReturn> {
             if self.values.read().len() == index {
-                let result = self.iterable.next(vm)?;
+                let result = match self.iterable.next(vm)? {
+                    PyIterReturn::Return(obj) => obj,
+                    PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+                };
                 self.values.write().push(result);
             }
-            Ok(self.values.read()[index].clone())
+            Ok(PyIterReturn::Return(self.values.read()[index].clone()))
         }
     }
 
@@ -999,10 +1052,13 @@ mod decl {
     }
     impl IteratorIterable for PyItertoolsTee {}
     impl SlotIterator for PyItertoolsTee {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-            let value = zelf.tee_data.get_item(vm, zelf.index.load())?;
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+            let value = match zelf.tee_data.get_item(vm, zelf.index.load())? {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            };
             zelf.index.fetch_add(1);
-            Ok(value)
+            Ok(PyIterReturn::Return(value))
         }
     }
 
@@ -1075,17 +1131,17 @@ mod decl {
     }
     impl IteratorIterable for PyItertoolsProduct {}
     impl SlotIterator for PyItertoolsProduct {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             // stop signal
             if zelf.stop.load() {
-                return Err(vm.new_stop_iteration());
+                return Ok(PyIterReturn::StopIteration(None));
             }
 
             let pools = &zelf.pools;
 
             for p in pools {
                 if p.is_empty() {
-                    return Err(vm.new_stop_iteration());
+                    return Ok(PyIterReturn::StopIteration(None));
                 }
             }
 
@@ -1100,7 +1156,7 @@ mod decl {
 
             zelf.update_idxs(idxs);
 
-            Ok(res)
+            Ok(PyIterReturn::Return(res))
         }
     }
 
@@ -1154,10 +1210,10 @@ mod decl {
     impl PyItertoolsCombinations {}
     impl IteratorIterable for PyItertoolsCombinations {}
     impl SlotIterator for PyItertoolsCombinations {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             // stop signal
             if zelf.exhausted.load() {
-                return Err(vm.new_stop_iteration());
+                return Ok(PyIterReturn::StopIteration(None));
             }
 
             let n = zelf.pool.len();
@@ -1165,7 +1221,7 @@ mod decl {
 
             if r == 0 {
                 zelf.exhausted.store(true);
-                return Ok(vm.ctx.new_tuple(vec![]));
+                return Ok(PyIterReturn::Return(vm.ctx.new_tuple(vec![])));
             }
 
             let res = vm.ctx.new_tuple(
@@ -1199,7 +1255,7 @@ mod decl {
                 }
             }
 
-            Ok(res)
+            Ok(PyIterReturn::Return(res))
         }
     }
 
@@ -1245,10 +1301,10 @@ mod decl {
 
     impl IteratorIterable for PyItertoolsCombinationsWithReplacement {}
     impl SlotIterator for PyItertoolsCombinationsWithReplacement {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             // stop signal
             if zelf.exhausted.load() {
-                return Err(vm.new_stop_iteration());
+                return Ok(PyIterReturn::StopIteration(None));
             }
 
             let n = zelf.pool.len();
@@ -1256,7 +1312,7 @@ mod decl {
 
             if r == 0 {
                 zelf.exhausted.store(true);
-                return Ok(vm.ctx.new_tuple(vec![]));
+                return Ok(PyIterReturn::Return(vm.ctx.new_tuple(vec![])));
             }
 
             let mut indices = zelf.indices.write();
@@ -1285,7 +1341,7 @@ mod decl {
                 }
             }
 
-            Ok(res)
+            Ok(PyIterReturn::Return(res))
         }
     }
 
@@ -1353,10 +1409,10 @@ mod decl {
     impl PyItertoolsPermutations {}
     impl IteratorIterable for PyItertoolsPermutations {}
     impl SlotIterator for PyItertoolsPermutations {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             // stop signal
             if zelf.exhausted.load() {
-                return Err(vm.new_stop_iteration());
+                return Ok(PyIterReturn::StopIteration(None));
             }
 
             let n = zelf.pool.len();
@@ -1364,7 +1420,7 @@ mod decl {
 
             if n == 0 {
                 zelf.exhausted.store(true);
-                return Ok(vm.ctx.new_tuple(vec![]));
+                return Ok(PyIterReturn::Return(vm.ctx.new_tuple(vec![])));
             }
 
             let mut result = zelf.result.write();
@@ -1401,20 +1457,22 @@ mod decl {
                 }
                 if !sentinel {
                     zelf.exhausted.store(true);
-                    return Err(vm.new_stop_iteration());
+                    return Ok(PyIterReturn::StopIteration(None));
                 }
             } else {
                 // On the first pass, initialize result tuple using the indices
                 *result = Some((0..r).collect());
             }
 
-            Ok(vm.ctx.new_tuple(
-                result
-                    .as_ref()
-                    .unwrap()
-                    .iter()
-                    .map(|&i| zelf.pool[i].clone())
-                    .collect(),
+            Ok(PyIterReturn::Return(
+                vm.ctx.new_tuple(
+                    result
+                        .as_ref()
+                        .unwrap()
+                        .iter()
+                        .map(|&i| zelf.pool[i].clone())
+                        .collect(),
+                ),
             ))
         }
     }
@@ -1451,30 +1509,27 @@ mod decl {
     impl PyItertoolsZipLongest {}
     impl IteratorIterable for PyItertoolsZipLongest {}
     impl SlotIterator for PyItertoolsZipLongest {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             if zelf.iterators.is_empty() {
-                Err(vm.new_stop_iteration())
+                Ok(PyIterReturn::StopIteration(None))
             } else {
                 let mut result: Vec<PyObjectRef> = Vec::new();
                 let mut numactive = zelf.iterators.len();
 
                 for idx in 0..zelf.iterators.len() {
-                    let next_obj = match zelf.iterators[idx].next(vm) {
-                        Ok(obj) => obj,
-                        Err(err) => {
-                            if !err.isinstance(&vm.ctx.exceptions.stop_iteration) {
-                                return Err(err);
-                            }
+                    let next_obj = match zelf.iterators[idx].next(vm)? {
+                        PyIterReturn::Return(obj) => obj,
+                        PyIterReturn::StopIteration(v) => {
                             numactive -= 1;
                             if numactive == 0 {
-                                return Err(vm.new_stop_iteration());
+                                return Ok(PyIterReturn::StopIteration(v));
                             }
                             zelf.fillvalue.clone()
                         }
                     };
                     result.push(next_obj);
                 }
-                Ok(vm.ctx.new_tuple(result))
+                Ok(PyIterReturn::Return(vm.ctx.new_tuple(result)))
             }
         }
     }
@@ -1503,14 +1558,20 @@ mod decl {
     impl PyItertoolsPairwise {}
     impl IteratorIterable for PyItertoolsPairwise {}
     impl SlotIterator for PyItertoolsPairwise {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let old = match zelf.old.read().clone() {
-                None => zelf.iterator.next(vm)?,
+                None => match zelf.iterator.next(vm)? {
+                    PyIterReturn::Return(obj) => obj,
+                    PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+                },
                 Some(obj) => obj,
             };
-            let new = zelf.iterator.next(vm)?;
+            let new = match zelf.iterator.next(vm)? {
+                PyIterReturn::Return(obj) => obj,
+                PyIterReturn::StopIteration(v) => return Ok(PyIterReturn::StopIteration(v)),
+            };
             *zelf.old.write() = Some(new.clone());
-            Ok(vm.ctx.new_tuple(vec![old, new]))
+            Ok(PyIterReturn::Return(vm.ctx.new_tuple(vec![old, new])))
         }
     }
 }

vm/src/stdlib/operator.rs

@@ -14,7 +14,7 @@ mod _operator {
         builtins::{PyInt, PyIntRef, PyStrRef, PyTypeRef},
         function::{ArgBytesLike, FuncArgs, KwArgs, OptionalArg},
         iterator,
-        protocol::PyIter,
+        protocol::{PyIter, PyIterReturn},
         slots::{
             Callable,
             PyComparisonOp::{Eq, Ge, Gt, Le, Lt, Ne},
@@ -220,7 +220,7 @@ mod _operator {
     #[pyfunction(name = "countOf")]
     fn count_of(a: PyIter, b: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
         let mut count: usize = 0;
-        while let Some(element) = iterator::get_next_object(vm, &a)? {
+        while let PyIterReturn::Return(element) = a.next(vm)? {
             if element.is(&b) || vm.bool_eq(&b, &element)? {
                 count += 1;
             }
@@ -244,7 +244,7 @@ mod _operator {
     #[pyfunction(name = "indexOf")]
     fn index_of(a: PyIter, b: PyObjectRef, vm: &VirtualMachine) -> PyResult<usize> {
         let mut index: usize = 0;
-        while let Some(element) = iterator::get_next_object(vm, &a)? {
+        while let PyIterReturn::Return(element) = a.next(vm)? {
             if element.is(&b) || vm.bool_eq(&b, &element)? {
                 return Ok(index);
             }

vm/src/stdlib/os.rs

@@ -430,6 +430,7 @@ pub(super) mod _os {
         crt_fd::{Fd, Offset},
         exceptions::IntoPyException,
         function::{ArgBytesLike, FuncArgs, OptionalArg},
+        protocol::PyIterReturn,
         slots::{IteratorIterable, SlotIterator},
         suppress_iph,
         utils::Either,
@@ -899,28 +900,30 @@ pub(super) mod _os {
     }
     impl IteratorIterable for ScandirIterator {}
     impl SlotIterator for ScandirIterator {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             if zelf.exhausted.load() {
-                return Err(vm.new_stop_iteration());
+                return Ok(PyIterReturn::StopIteration(None));
             }
 
             match zelf.entries.write().next() {
                 Some(entry) => match entry {
-                    Ok(entry) => Ok(DirEntry {
-                        entry,
-                        mode: zelf.mode,
-                        lstat: OnceCell::new(),
-                        stat: OnceCell::new(),
-                        #[cfg(not(unix))]
-                        ino: AtomicCell::new(None),
-                    }
-                    .into_ref(vm)
-                    .into_object()),
+                    Ok(entry) => Ok(PyIterReturn::Return(
+                        DirEntry {
+                            entry,
+                            mode: zelf.mode,
+                            lstat: OnceCell::new(),
+                            stat: OnceCell::new(),
+                            #[cfg(not(unix))]
+                            ino: AtomicCell::new(None),
+                        }
+                        .into_ref(vm)
+                        .into_object(),
+                    )),
                     Err(err) => Err(err.into_pyexception(vm)),
                 },
                 None => {
                     zelf.exhausted.store(true);
-                    Err(vm.new_stop_iteration())
+                    Ok(PyIterReturn::StopIteration(None))
                 }
             }
         }

vm/src/stdlib/pystruct.rs

@@ -18,6 +18,7 @@ pub(crate) mod _struct {
         },
         common::str::wchar_t,
         function::{ArgBytesLike, ArgMemoryBuffer, PosArgs},
+        protocol::PyIterReturn,
         slots::{IteratorIterable, SlotConstructor, SlotIterator},
         utils::Either,
         IntoPyObject, PyObjectRef, PyRef, PyResult, PyValue, TryFromObject, VirtualMachine,
@@ -832,14 +833,16 @@ pub(crate) mod _struct {
     }
     impl IteratorIterable for UnpackIterator {}
     impl SlotIterator for UnpackIterator {
-        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
+        fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
             let size = zelf.format_spec.size;
             let offset = zelf.offset.fetch_add(size);
             zelf.buffer.with_ref(|buf| {
                 if let Some(buf) = buf.get(offset..offset + size) {
-                    zelf.format_spec.unpack(buf, vm).map(|x| x.into_object())
+                    zelf.format_spec
+                        .unpack(buf, vm)
+                        .map(|x| PyIterReturn::Return(x.into_object()))
                 } else {
-                    Err(vm.new_stop_iteration())
+                    Ok(PyIterReturn::StopIteration(None))
                 }
             })
         }

vm/src/vm.rs

@@ -22,6 +22,7 @@ use crate::{
     frozen,
     function::{FuncArgs, IntoFuncArgs},
     import, iterator,
+    protocol::PyIterReturn,
     scope::Scope,
     signal::NSIG,
     slots::PyComparisonOp,
@@ -1927,7 +1928,7 @@ impl VirtualMachine {
     fn _membership_iter_search(&self, haystack: PyObjectRef, needle: PyObjectRef) -> PyResult {
         let iter = haystack.get_iter(self)?;
         loop {
-            if let Some(element) = iterator::get_next_object(self, &iter)? {
+            if let PyIterReturn::Return(element) = iter.next(self)? {
                 if self.bool_eq(&needle, &element)? {
                     return Ok(self.ctx.new_bool(true));
                 } else {

wasm/lib/src/js_module.rs

@@ -6,15 +6,15 @@ use std::{cell, fmt, future};
 use wasm_bindgen::{closure::Closure, prelude::*, JsCast};
 use wasm_bindgen_futures::{future_to_promise, JsFuture};
 
-use rustpython_vm::builtins::PyBaseExceptionRef;
-use rustpython_vm::builtins::{PyFloatRef, PyStrRef, PyTypeRef};
-use rustpython_vm::function::{OptionalArg, OptionalOption, PosArgs};
-use rustpython_vm::slots::{IteratorIterable, SlotIterator};
-use rustpython_vm::types::create_simple_type;
-use rustpython_vm::VirtualMachine;
 use rustpython_vm::{
-    function::ArgCallable, IntoPyObject, PyClassImpl, PyObjectRef, PyRef, PyResult, PyValue,
-    TryFromObject,
+    builtins::{PyBaseExceptionRef, PyFloatRef, PyStrRef, PyTypeRef},
+    function::ArgCallable,
+    function::{OptionalArg, OptionalOption, PosArgs},
+    protocol::PyIterReturn,
+    slots::{IteratorIterable, SlotIterator},
+    types::create_simple_type,
+    IntoPyObject, PyClassImpl, PyObjectRef, PyRef, PyResult, PyValue, TryFromObject,
+    VirtualMachine,
 };
 
 #[wasm_bindgen(inline_js = "
@@ -589,8 +589,8 @@ impl AwaitPromise {
 
 impl IteratorIterable for AwaitPromise {}
 impl SlotIterator for AwaitPromise {
-    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
-        zelf.send(None, vm)
+    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult<PyIterReturn> {
+        PyIterReturn::from_result(zelf.send(None, vm), vm)
     }
 }