https://github.com/python/cpython/commit/814ac0d58789fd544855a6c1afb9d89a690a0c3b
commit: 814ac0d58789fd544855a6c1afb9d89a690a0c3b
branch: 3.13
author: Mark Shannon <m...@hotpy.org>
committer: markshannon <m...@hotpy.org>
date: 2025-05-27T14:12:04+01:00
summary:
[3.13] gh-128161: Remove redundant GET_ITER from list comprehension code
(backport of GH-134778) (GH-134788)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2025-05-27-09-19-21.gh-issue-127682.9WwFrM.rst
M Lib/test/test_coroutines.py
M Lib/test/test_listcomps.py
M Python/compile.c
diff --git a/Lib/test/test_coroutines.py b/Lib/test/test_coroutines.py
index f705f4f5bfbd88..77cdbf98067e8c 100644
--- a/Lib/test/test_coroutines.py
+++ b/Lib/test/test_coroutines.py
@@ -2252,6 +2252,31 @@ 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 45644d6c092782..23fa5ef4f43810 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/compile.c b/Python/compile.c
index e8d19d2dc42744..dba10237a2a735 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -5501,9 +5501,9 @@ compiler_async_comprehension_generator(struct 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 */
@@ -5790,19 +5790,6 @@ pop_inlined_comprehension_state(struct compiler *c,
location loc,
return SUCCESS;
}
-static inline int
-compiler_comprehension_iter(struct 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
compiler_comprehension(struct compiler *c, expr_ty e, int type,
identifier name, asdl_comprehension_seq *generators,
expr_ty elt,
@@ -5824,9 +5811,7 @@ compiler_comprehension(struct compiler *c, expr_ty e, int
type,
outermost = (comprehension_ty) asdl_seq_GET(generators, 0);
if (is_inlined) {
- if (compiler_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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