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Fix unpack msg #7175

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Merged
youknowone merged 1 commit into from
Feb 17, 2026
Merged

Fix unpack msg #7175

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14 changes: 7 additions & 7 deletions Lib/test/test_unpack.py
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Original file line number Diff line number Diff line change
Expand Up @@ -70,14 +70,14 @@

Unpacking tuple of wrong size

>>> a, b = t # TODO: RUSTPYTHON # doctest: +EXPECTED_FAILURE
>>> a, b = t
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 2, got 3)

Unpacking tuple of wrong size

>>> a, b = l # TODO: RUSTPYTHON # doctest: +EXPECTED_FAILURE
>>> a, b = l
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 2, got 3)
Expand Down Expand Up @@ -144,7 +144,7 @@

Unpacking to an empty iterable should raise ValueError

>>> () = [42] # TODO: RUSTPYTHON # doctest: +EXPECTED_FAILURE
>>> () = [42]
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 0, got 1)
Expand All @@ -157,13 +157,13 @@
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 3)
>>> next(it) # TODO: RUSTPYTHON; Raise `StopIteration` # doctest: +SKIP
>>> next(it)
4

Unpacking unbalanced dict

>>> d = {4: 'four', 5: 'five', 6: 'six', 7: 'seven'}
>>> a, b, c = d # TODO: RUSTPYTHON; # doctest: +EXPECTED_FAILURE
>>> a, b, c = d
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 3, got 4)
Expand All @@ -176,7 +176,7 @@
... def __getitem__(self, i):
... return i*2
...
>>> x, y, z = LengthTooLong() # TODO: RUSTPYTHON; Hangs # doctest: +SKIP
>>> x, y, z = LengthTooLong()
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 3)
Expand All @@ -189,7 +189,7 @@
... def __getitem__(self, i):
... return i*2
...
>>> x, y, z = BadLength() # TODO: RUSTPYTHON; Hangs # doctest: +SKIP
>>> x, y, z = BadLength()
Traceback (most recent call last):
...
ValueError: too many values to unpack (expected 3)
Expand Down
95 changes: 80 additions & 15 deletions crates/vm/src/frame.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3043,13 +3043,54 @@ impl ExecutingFrame<'_> {
Ok(None)
}

/// _PyEval_UnpackIterableStackRef
fn unpack_sequence(&mut self, size: u32, vm: &VirtualMachine) -> FrameResult {
let value = self.pop_value();
let size = size as usize;

// Fast path for exact tuple/list types (not subclasses) — check
// length directly without creating an iterator, matching
// UNPACK_SEQUENCE_TUPLE / UNPACK_SEQUENCE_LIST specializations.
let cls = value.class();
let fast_elements: Option<Vec<PyObjectRef>> = if cls.is(vm.ctx.types.tuple_type) {
Some(value.downcast_ref::<PyTuple>().unwrap().as_slice().to_vec())
} else if cls.is(vm.ctx.types.list_type) {
Some(
value
.downcast_ref::<PyList>()
.unwrap()
.borrow_vec()
.to_vec(),
)
} else {
None
};
if let Some(elements) = fast_elements {
return match elements.len().cmp(&size) {
core::cmp::Ordering::Equal => {
self.state
.stack
.extend(elements.into_iter().rev().map(Some));
Ok(None)
}
core::cmp::Ordering::Greater => Err(vm.new_value_error(format!(
"too many values to unpack (expected {size}, got {})",
elements.len()
))),
core::cmp::Ordering::Less => Err(vm.new_value_error(format!(
"not enough values to unpack (expected {size}, got {})",
elements.len()
))),
};
}

// General path — iterate up to `size + 1` elements to avoid
// consuming the entire iterator (fixes hang on infinite sequences).
let not_iterable = value.class().slots.iter.load().is_none()
&& value
.get_class_attr(vm.ctx.intern_str("__getitem__"))
.is_none();
let elements: Vec<_> = value.try_to_value(vm).map_err(|e| {
let iter = PyIter::try_from_object(vm, value.clone()).map_err(|e| {
if not_iterable && e.class().is(vm.ctx.exceptions.type_error) {
vm.new_type_error(format!(
"cannot unpack non-iterable {} object",
Expand All @@ -3059,24 +3100,48 @@ impl ExecutingFrame<'_> {
e
}
})?;
let msg = match elements.len().cmp(&(size as usize)) {
core::cmp::Ordering::Equal => {
// Wrap each element in Some() for Option<PyObjectRef> stack

let mut elements = Vec::with_capacity(size);
for _ in 0..size {
match iter.next(vm)? {
PyIterReturn::Return(item) => elements.push(item),
PyIterReturn::StopIteration(_) => {
return Err(vm.new_value_error(format!(
"not enough values to unpack (expected {size}, got {})",
elements.len()
)));
}
}
}

// Check that the iterator is exhausted.
match iter.next(vm)? {
PyIterReturn::Return(_) => {
// For exact dict types, show "got N" using the container's
// size (PyDict_Size). Exact tuple/list are handled by the
// fast path above and never reach here.
let msg = if value.class().is(vm.ctx.types.dict_type) {
if let Ok(got) = value.length(vm) {
if got > size {
format!("too many values to unpack (expected {size}, got {got})")
} else {
format!("too many values to unpack (expected {size})")
}
} else {
format!("too many values to unpack (expected {size})")
}
} else {
format!("too many values to unpack (expected {size})")
};
Err(vm.new_value_error(msg))
}
PyIterReturn::StopIteration(_) => {
self.state
.stack
.extend(elements.into_iter().rev().map(Some));
return Ok(None);
}
core::cmp::Ordering::Greater => {
format!("too many values to unpack (expected {size})")
Ok(None)
}
core::cmp::Ordering::Less => format!(
"not enough values to unpack (expected {}, got {})",
size,
elements.len()
),
};
Err(vm.new_value_error(msg))
}
}

fn convert_value(
Expand Down
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