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remove redundant counters for remaining elements in set and frozenset iteration #5726

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Merged
davidhewitt merged 4 commits into from
Jan 11, 2026
Merged

remove redundant counters for remaining elements in set and frozenset iteration #5726

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aa0b658
don't count remaining elements in set and frozenset iteration
davidhewitt Jan 9, 2026
5a51f0d
Merge branch 'PyO3:main' into set-size-hint
davidhewitt Jan 10, 2026
6817a6a
make call to `ExactSizeIterator` implementation more explicit
davidhewitt Jan 11, 2026
95718b5
newsfragment
davidhewitt Jan 11, 2026
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21 changes: 8 additions & 13 deletions src/types/frozenset.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -188,18 +188,11 @@ impl<'py> IntoIterator for &Bound<'py, PyFrozenSet> {
}

/// PyO3 implementation of an iterator for a Python `frozenset` object.
pub struct BoundFrozenSetIterator<'p> {
it: Bound<'p, PyIterator>,
// Remaining elements in the frozenset
remaining: usize,
}
pub struct BoundFrozenSetIterator<'py>(Bound<'py, PyIterator>);

impl<'py> BoundFrozenSetIterator<'py> {
pub(super) fn new(set: Bound<'py, PyFrozenSet>) -> Self {
Self {
it: PyIterator::from_object(&set).unwrap(),
remaining: set.len(),
}
Self(PyIterator::from_object(&set).expect("frozenset should always be iterable"))
}
}

Expand All @@ -208,12 +201,14 @@ impl<'py> Iterator for BoundFrozenSetIterator<'py> {

/// Advances the iterator and returns the next value.
fn next(&mut self) -> Option<Self::Item> {
self.remaining = self.remaining.saturating_sub(1);
self.it.next().map(Result::unwrap)
self.0
.next()
.map(|result| result.expect("frozenset iteration should be infallible"))
}

fn size_hint(&self) -> (usize, Option<usize>) {
(self.remaining, Some(self.remaining))
let len = self.len();
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@LilyFirefly LilyFirefly Jan 10, 2026

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Do we need to call self.__length_hint__() here? (Or whatever the Rust/C name of that is.)

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@davidhewitt davidhewitt Jan 11, 2026

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Changed to call ExactSizeIterator::len to show where this value is coming from (that len does call size_hint of the underlying iterator, yes).

(len, Some(len))
}

#[inline]
Expand All @@ -227,7 +222,7 @@ impl<'py> Iterator for BoundFrozenSetIterator<'py> {

impl ExactSizeIterator for BoundFrozenSetIterator<'_> {
fn len(&self) -> usize {
self.remaining
self.0.size_hint().0
}
}

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22 changes: 8 additions & 14 deletions src/types/set.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -222,19 +222,11 @@ impl<'py> IntoIterator for &Bound<'py, PySet> {
}

/// PyO3 implementation of an iterator for a Python `set` object.
pub struct BoundSetIterator<'p> {
it: Bound<'p, PyIterator>,
// Remaining elements in the set. This is fine to store because
// Python will error if the set changes size during iteration.
remaining: usize,
}
pub struct BoundSetIterator<'py>(Bound<'py, PyIterator>);

impl<'py> BoundSetIterator<'py> {
pub(super) fn new(set: Bound<'py, PySet>) -> Self {
Self {
it: PyIterator::from_object(&set).unwrap(),
remaining: set.len(),
}
Self(PyIterator::from_object(&set).expect("set should always be iterable"))
}
}

Expand All @@ -243,12 +235,14 @@ impl<'py> Iterator for BoundSetIterator<'py> {

/// Advances the iterator and returns the next value.
fn next(&mut self) -> Option<Self::Item> {
self.remaining = self.remaining.saturating_sub(1);
self.it.next().map(Result::unwrap)
self.0
.next()
.map(|result| result.expect("set iteration should be infallible"))
}

fn size_hint(&self) -> (usize, Option<usize>) {
(self.remaining, Some(self.remaining))
let len = self.len();
(len, Some(len))
}

#[inline]
Expand All @@ -262,7 +256,7 @@ impl<'py> Iterator for BoundSetIterator<'py> {

impl ExactSizeIterator for BoundSetIterator<'_> {
fn len(&self) -> usize {
self.remaining
self.0.size_hint().0
}
}

Expand Down
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