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Check n before iter() in itertools.tee() and re-check the iterator #9518

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Merged
youknowone merged 1 commit into from
Nov 1, 2026
Merged

Check n before iter() in itertools.tee() and re-check the iterator #9518

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16 changes: 8 additions & 8 deletions crates/vm/src/stdlib/itertools.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1106,6 +1106,8 @@ mod decl {

impl PyItertoolsTee {
fn from_iter(iterator: PyIter, vm: &VirtualMachine) -> PyResult {
// An iterator is asked for its iterator again, which validates its __iter__.
let iterator = iterator.get_iter(vm)?;
let class = Self::class(&vm.ctx);
if iterator.class().is(class) {
return vm.call_special_method(&iterator, identifier!(vm, __copy__), ());
Expand Down Expand Up @@ -1138,7 +1140,7 @@ mod decl {
#[derive(FromArgs)]
struct TeeArgs {
#[pyarg(positional)]
iterable: PyIter,
iterable: PyObjectRef,
#[pyarg(positional, default = 2)]
n: isize,
}
Expand All @@ -1151,17 +1153,15 @@ mod decl {
}
let n = n as usize;

// Only an iterator that cannot copy itself needs a tee to buffer it.
let copyable = if iterable.class().has_attr(identifier!(vm, __copy__)) {
iterable.into()
} else {
PyItertoolsTee::from_iter(iterable, vm)?
};

let mut tee_vec: Vec<PyObjectRef> = Vec::new();
tee_vec
.try_reserve_exact(n)
.map_err(|_| vm.no_memory_error())?;
if n == 0 {
return Ok(vm.ctx.empty_tuple.clone());
}

let copyable = PyItertoolsTee::from_iter(iterable.get_iter(vm)?, vm)?;
for _ in 0..n {
tee_vec.push(vm.call_special_method(&copyable, identifier!(vm, __copy__), ())?);
}
Expand Down
42 changes: 42 additions & 0 deletions extra_tests/snippets/stdlib_itertools.py
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Original file line number Diff line number Diff line change
Expand Up @@ -367,6 +367,48 @@ def assert_matches_seq(it, seq):
assert list(t[0]) == [1, 2, 3]
assert list(t[0]) == []


class NoneIter:
def __iter__(self):
return None


with assert_raises(ValueError):
itertools.tee(NoneIter(), -1)
assert itertools.tee(NoneIter(), 0) == ()


class BadIterator:
def __iter__(self):
return None

def __next__(self):
return None


class BadIterable:
def __iter__(self):
return BadIterator()


with assert_raises(TypeError):
itertools.tee(BadIterable())


class CopyRaisingIterator:
def __iter__(self):
return self

def __next__(self):
raise StopIteration

def __copy__(self):
raise RuntimeError


t0, t1 = itertools.tee(CopyRaisingIterator())
assert list(t0) == list(t1) == []

# itertools.product

product_source = iter([1])
Expand Down
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