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gh-150700: Fix class-scope inline comprehensions when nested scopes reference __class__ and friends #150735

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gh-150700: Fix class-scope inline comprehensions when nested scopes reference __class__ and friends #150735

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43d91fd
Fix class-scope inline comprehensions when nested scopes reference `_…
johnslavik Jun 1, 2026
6e4dec5
Merge branch 'main' into gh-150700-class-scope-comprehension-with-lam…
johnslavik Jun 1, 2026
903f916
Fix tests
johnslavik Jun 1, 2026
e2547b8
Fix typo
johnslavik Jun 1, 2026
633c54c
Fix formatting
johnslavik Jun 1, 2026
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26 changes: 26 additions & 0 deletions Lib/test/test_listcomps.py
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Original file line number Diff line number Diff line change
Expand Up @@ -171,6 +171,12 @@ def test_references___class__(self):
"""
self._check_in_scopes(code, raises=NameError)

def test_references___class___nested(self):
code = """
res = [lambda: __class__ for _ in [1]]
"""
self._check_in_scopes(code, raises=NameError)

def test_references___class___defined(self):
code = """
__class__ = 2
Expand All @@ -180,18 +186,38 @@ def test_references___class___defined(self):
code, outputs={"res": [2]}, scopes=["module", "function"])
self._check_in_scopes(code, raises=NameError, scopes=["class"])

def test_references___class___defined_nested(self):
code = """
__class__ = 2
res = [(lambda: __class__)() for x in [1]]
"""
self._check_in_scopes(
code, outputs={"res": [2]}, scopes=["module", "function"])
self._check_in_scopes(code, raises=NameError, scopes=["class"])

def test_references___classdict__(self):
code = """
class i: [__classdict__ for x in y]
"""
self._check_in_scopes(code, raises=NameError)

def test_references___classdict___nested(self):
class _C:
res = [(lambda: __classdict__)() for _ in [1]]
self.assertIn("res", _C.res[0])

def test_references___conditional_annotations__(self):
code = """
class i: [__conditional_annotations__ for x in y]
"""
self._check_in_scopes(code, raises=NameError)

def test_references___conditional_annotations___nested(self):
code = """
class i: [lambda: __conditional_annotations__ for x in y]
"""
self._check_in_scopes(code, raises=NameError)

def test_references___class___enclosing(self):
code = """
__class__ = 2
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-06-01-19-00-00.gh-issue-150700.W8CzVR.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix a :exc:`SystemError` when compiling a class-scope comprehension containing
a ``lambda`` that references ``__class__``, ``__classdict__``, or
``__conditional_annotations__``. Patch by Bartosz Sławecki.
Comment on lines +2 to +3
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@ZeroIntensity ZeroIntensity Jun 2, 2026

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I would only mention __class__ here, since __classdict__ and __conditional_annotations__ are internal-only.

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@johnslavik johnslavik Jun 2, 2026 •
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Thanks.

I'm of two minds on this. I initially wrote this news entry to indeed include __class__ only, but then I looked up that we already have a precedent news entry that does mention both __classdict__ and __conditional_annotations__. Both aren't of likely special interest to the regular user, but they are of interest to me or others who know it and I liked the transparency. Maybe it's ok to keep it?

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@ZeroIntensity ZeroIntensity Jun 2, 2026

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Sure, I'm just being nitpicky. I don't necessarily agree with that precedent, FWIW. The changelog should be for users, not maintainers -- maintainers can read the commit log if they care.

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@JelleZijlstra JelleZijlstra Jun 2, 2026

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I do think we should mention all. The changelog can be fairly low-level and should mention changes that are visible to end users, even end users poking into things they probably shouldn't be poking into.

13 changes: 9 additions & 4 deletions Python/symtable.c
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Original file line number Diff line number Diff line change
Expand Up @@ -834,17 +834,22 @@ inline_comprehension(PySTEntryObject *ste, PySTEntryObject *comp,
return 0;
}
// __class__, __classdict__ and __conditional_annotations__ are
// never allowed to be free through a class scope (see
// drop_class_free)
// not allowed to be free through a class scope (see
// drop_class_free) unless children scopes need it
if (scope == FREE && ste->ste_type == ClassBlock &&
(_PyUnicode_EqualToASCIIString(k, "__class__") ||
_PyUnicode_EqualToASCIIString(k, "__classdict__") ||
_PyUnicode_EqualToASCIIString(k, "__conditional_annotations__"))) {
scope = GLOBAL_IMPLICIT;
if (PySet_Discard(comp_free, k) < 0) {
int child_needs_free = is_free_in_any_child(comp, k);
if (child_needs_free < 0) {
return 0;
}

if (!child_needs_free) {
if (PySet_Discard(comp_free, k) < 0) {
return 0;
}
}
if (_PyUnicode_EqualToASCIIString(k, "__class__")) {
remove_dunder_class = 1;
}
Expand Down
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