diff --git a/Lib/test/test_coroutines.py b/Lib/test/test_coroutines.py
index 4755046fe1904d..c8360a834482e1 100644
--- a/Lib/test/test_coroutines.py
+++ b/Lib/test/test_coroutines.py
@@ -2265,6 +2265,31 @@ def c():
# before fixing, visible stack from throw would be shorter than from send.
self.assertEqual(len_send, len_throw)
+ def test_call_aiter_once_in_comprehension(self):
+
+ class Iterator:
+
+ def __init__(self):
+ self.val = 0
+
+ async def __anext__(self):
+ if self.val == 2:
+ raise StopAsyncIteration
+ self.val += 1
+ return self.val
+
+ # No __aiter__ method
+
+ class C:
+
+ def __aiter__(self):
+ return Iterator()
+
+ async def run():
+ return [i async for i in C()]
+
+ self.assertEqual(run_async(run()), ([], [1,2]))
+
@unittest.skipIf(
support.is_emscripten or support.is_wasi,
diff --git a/Lib/test/test_listcomps.py b/Lib/test/test_listcomps.py
index cffdeeacc5d73b..38a36d3c9925a2 100644
--- a/Lib/test/test_listcomps.py
+++ b/Lib/test/test_listcomps.py
@@ -750,6 +750,28 @@ def iter_raises():
self.assertEqual(f.line[f.colno - indent : f.end_colno - indent],
expected)
+ def test_only_calls_dunder_iter_once(self):
+
+ class Iterator:
+
+ def __init__(self):
+ self.val = 0
+
+ def __next__(self):
+ if self.val == 2:
+ raise StopIteration
+ self.val += 1
+ return self.val
+
+ # No __iter__ method
+
+ class C:
+
+ def __iter__(self):
+ return Iterator()
+
+ self.assertEqual([1,2], [i for i in C()])
+
__test__ = {'doctests' : doctests}
def load_tests(loader, tests, pattern):
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-05-27-09-19-21.gh-issue-127682.9WwFrM.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-05-27-09-19-21.gh-issue-127682.9WwFrM.rst
new file mode 100644
index 00000000000000..ca0a694dfaaef8
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-05-27-09-19-21.gh-issue-127682.9WwFrM.rst
@@ -0,0 +1,2 @@
+No longer call ``__iter__`` twice in list comprehensions. This brings the
+behavior of list comprehensions in line with other forms of iteration
diff --git a/Python/codegen.c b/Python/codegen.c
index 683601103ec99d..1672b655fa9423 100644
--- a/Python/codegen.c
+++ b/Python/codegen.c
@@ -4543,9 +4543,9 @@ codegen_async_comprehension_generator(compiler *c, location loc,
else {
/* Sub-iter - calculate on the fly */
VISIT(c, expr, gen->iter);
- ADDOP(c, LOC(gen->iter), GET_AITER);
}
}
+ ADDOP(c, LOC(gen->iter), GET_AITER);
USE_LABEL(c, start);
/* Runtime will push a block here, so we need to account for that */
@@ -4757,19 +4757,6 @@ pop_inlined_comprehension_state(compiler *c, location loc,
return SUCCESS;
}
-static inline int
-codegen_comprehension_iter(compiler *c, comprehension_ty comp)
-{
- VISIT(c, expr, comp->iter);
- if (comp->is_async) {
- ADDOP(c, LOC(comp->iter), GET_AITER);
- }
- else {
- ADDOP(c, LOC(comp->iter), GET_ITER);
- }
- return SUCCESS;
-}
-
static int
codegen_comprehension(compiler *c, expr_ty e, int type,
identifier name, asdl_comprehension_seq *generators, expr_ty elt,
@@ -4789,9 +4776,7 @@ codegen_comprehension(compiler *c, expr_ty e, int type,
outermost = (comprehension_ty) asdl_seq_GET(generators, 0);
if (is_inlined) {
- if (codegen_comprehension_iter(c, outermost)) {
- goto error;
- }
+ VISIT(c, expr, outermost->iter);
if (push_inlined_comprehension_state(c, loc, entry, &inline_state)) {
goto error;
}
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