https://github.com/python/cpython/commit/132bdf6990003df61d30c379a12c041010d00245
commit: 132bdf6990003df61d30c379a12c041010d00245
branch: 3.13
author: Mark Shannon <[email protected]>
committer: markshannon <[email protected]>
date: 2025-04-29T09:35:29+01:00
summary:
[3.13] GH-127682: Backport GH-132351 (GH-132384)
Only call `__iter__` once in generator expressions
files:
A Misc/NEWS.d/next/Core and
Builtins/2025-04-10-10-29-45.gh-issue-127682.X0HoGz.rst
M Lib/test/test_dis.py
M Lib/test/test_generators.py
M Lib/test/test_genexps.py
M Python/compile.c
diff --git a/Lib/test/test_dis.py b/Lib/test/test_dis.py
index 73807d7fa95fbd..51e00418165467 100644
--- a/Lib/test/test_dis.py
+++ b/Lib/test/test_dis.py
@@ -184,7 +184,6 @@ def bug1333982(x=[]):
LOAD_CONST 1 (<code object <genexpr> at 0x...,
file "%s", line %d>)
MAKE_FUNCTION
LOAD_FAST 0 (x)
- GET_ITER
CALL 0
%3d LOAD_CONST 2 (1)
@@ -765,7 +764,6 @@ def foo(x):
MAKE_FUNCTION
SET_FUNCTION_ATTRIBUTE 8 (closure)
LOAD_DEREF 1 (y)
- GET_ITER
CALL 0
CALL 1
RETURN_VALUE
diff --git a/Lib/test/test_generators.py b/Lib/test/test_generators.py
index 515fe7407f1d80..a6c1dd62a23cc3 100644
--- a/Lib/test/test_generators.py
+++ b/Lib/test/test_generators.py
@@ -246,6 +246,28 @@ def loop():
#This should not raise
loop()
+ def test_genexpr_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], list(i for i in C()))
+
class ModifyUnderlyingIterableTest(unittest.TestCase):
iterables = [
diff --git a/Lib/test/test_genexps.py b/Lib/test/test_genexps.py
index 4f2d3cdcc7943e..bb241837bd6679 100644
--- a/Lib/test/test_genexps.py
+++ b/Lib/test/test_genexps.py
@@ -123,15 +123,6 @@
>>> list(g)
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
-Verify that the outermost for-expression makes an immediate check
-for iterability
-
- >>> (i for i in 6)
- Traceback (most recent call last):
- File "<pyshell#4>", line 1, in -toplevel-
- (i for i in 6)
- TypeError: 'int' object is not iterable
-
Verify late binding for the outermost if-expression
>>> include = (2,4,6,8)
diff --git a/Misc/NEWS.d/next/Core and
Builtins/2025-04-10-10-29-45.gh-issue-127682.X0HoGz.rst b/Misc/NEWS.d/next/Core
and Builtins/2025-04-10-10-29-45.gh-issue-127682.X0HoGz.rst
new file mode 100644
index 00000000000000..b87750eb516e7a
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and
Builtins/2025-04-10-10-29-45.gh-issue-127682.X0HoGz.rst
@@ -0,0 +1,4 @@
+No longer call ``__iter__`` twice when creating and executing a generator
expression.
+Creating a generator expression from a non-interable will raise only when the
+generator expression is executed.
+This brings the behavior of generator expressions in line with other
generators.
diff --git a/Python/compile.c b/Python/compile.c
index bb2c2293a38c9a..e8d19d2dc42744 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -5910,9 +5910,7 @@ compiler_comprehension(struct compiler *c, expr_ty e, int
type,
}
Py_CLEAR(co);
- if (compiler_comprehension_iter(c, outermost)) {
- goto error;
- }
+ VISIT(c, expr, outermost->iter);
ADDOP_I(c, loc, CALL, 0);
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