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Check enumerate() arguments before calling __iter__ #9241

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Check enumerate() arguments before calling __iter__ #9241

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6 changes: 4 additions & 2 deletions crates/vm/src/builtins/enumerate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,8 +54,9 @@ impl PyPayload for PyEnumerate {

#[derive(FromArgs)]
pub struct EnumerateArgs {
// Bound as an object so the other arguments are checked before `iter()` runs, as in CPython.
#[pyarg(any)]
iterable: PyIter,
iterable: PyObjectRef,

@chatgpt-codex-connector chatgpt-codex-connector Bot Oct 20, 2026

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P2 Badge Defer start conversion until binding validates the call

After only iterable is made raw, a malformed call such as enumerate(BadIter(), RaisingIndex(), extra) reaches ArgIndex::try_from_object for start before FuncArgs::bind_for notices the extra positional argument. It therefore runs and may propagate RaisingIndex.__index__ instead of raising the argument-count TypeError; CPython rejects this call before invoking either __index__ or __iter__. Binding start as an object too, then converting it in py_new immediately before get_iter, preserves the intended valid-call order without this side effect.

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#[pyarg(any, default = 0)]
start: ArgIndex,
}
Expand All @@ -66,8 +67,9 @@ impl Constructor for PyEnumerate {
fn py_new(
_cls: &Py<PyType>,
Self::Args { iterable, start }: Self::Args,
_vm: &VirtualMachine,
vm: &VirtualMachine,
) -> PyResult<Self> {
let iterable = iterable.get_iter(vm)?;
let start = start.into_int_ref();
let counter = match start.as_bigint().to_usize() {
Some(n) => Counter::Small(n),
Expand Down
10 changes: 10 additions & 0 deletions extra_tests/snippets/builtin_enumerate.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
from testutils import TestFailingIter, assert_raises

assert list(enumerate(["a", "b", "c"])) == [(0, "a"), (1, "b"), (2, "c")]

assert type(enumerate([])) == enumerate
Expand Down Expand Up @@ -25,3 +27,11 @@ def __iter__(self):
it = enumerate(Counter())
assert next(it) == (0, 1)
assert next(it) == (1, 2)


# start and the argument count are checked before iter() is called
assert_raises(TypeError, enumerate, TestFailingIter(), {})
assert_raises(TypeError, enumerate, TestFailingIter(), 0, 0)
assert_raises(TypeError, enumerate, TestFailingIter(), foo=1)
assert_raises(TypeError, enumerate, iterable=TestFailingIter(), start={})
assert_raises(RuntimeError, enumerate, TestFailingIter(), 0)
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