https://github.com/python/cpython/commit/dd36d014da20f6217f0ae729450dd79745545927
commit: dd36d014da20f6217f0ae729450dd79745545927
branch: 3.14
author: Miss Islington (bot) <[email protected]>
committer: iritkatriel <[email protected]>
date: 2026-09-05T16:27:05Z
summary:
[3.14] gh-156091: Fix crash compiling deeply nested inlined comprehensions
(GH-156957) (#156993)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-09-04-14-06-00.gh-issue-156091.nested-comp.rst
M Include/internal/pycore_compile.h
M Lib/test/test_syntax.py
M Python/codegen.c
diff --git a/Include/internal/pycore_compile.h
b/Include/internal/pycore_compile.h
index ed776bbb73a0ee9..193d5d180a3c8cf 100644
--- a/Include/internal/pycore_compile.h
+++ b/Include/internal/pycore_compile.h
@@ -106,6 +106,7 @@ enum _PyCompile_FBlockType {
COMPILE_FBLOCK_EXCEPTION_HANDLER,
COMPILE_FBLOCK_EXCEPTION_GROUP_HANDLER,
COMPILE_FBLOCK_ASYNC_COMPREHENSION_GENERATOR,
+ COMPILE_FBLOCK_INLINED_COMPREHENSION,
COMPILE_FBLOCK_STOP_ITERATION,
};
diff --git a/Lib/test/test_syntax.py b/Lib/test/test_syntax.py
index de8c94fe8d2d18c..c11822333f4c7eb 100644
--- a/Lib/test/test_syntax.py
+++ b/Lib/test/test_syntax.py
@@ -3225,6 +3225,21 @@ def test_syntax_error_on_deeply_nested_blocks(self):
"""
self._check_error(source, "too many statically nested blocks")
+ @support.cpython_only
+ def test_nested_inlined_comprehensions_block_limit(self):
+ # Each inlined comprehension with locals emits SETUP_FINALLY, which
+ # must count toward CO_MAXBLOCKS (gh-156091).
+ def src(depth):
+ e = "i for i in r"
+ for _ in range(depth - 1):
+ e = "[" + e + "] for i in r"
+ return "x = [" + e + "]"
+
+ CO_MAXBLOCKS = 21
+ compile(src(CO_MAXBLOCKS), "<testcase>", "exec")
+ self._check_error(src(CO_MAXBLOCKS + 1),
+ "too many statically nested blocks")
+
@support.cpython_only
def test_error_on_parser_stack_overflow(self):
source = "-" * 100000 + "4"
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-09-04-14-06-00.gh-issue-156091.nested-comp.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-09-04-14-06-00.gh-issue-156091.nested-comp.rst
new file mode 100644
index 000000000000000..fdceb3209b7f7cb
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-09-04-14-06-00.gh-issue-156091.nested-comp.rst
@@ -0,0 +1,3 @@
+Fix a crash when compiling deeply nested inlined list, set, or dict
+comprehensions. A :exc:`SyntaxError` is now raised when the nesting exceeds
+the compiler's static block limit.
diff --git a/Python/codegen.c b/Python/codegen.c
index f90ec1756cdeab5..0aa9995b4f087f3 100644
--- a/Python/codegen.c
+++ b/Python/codegen.c
@@ -527,6 +527,7 @@ codegen_unwind_fblock(compiler *c, location *ploc,
case COMPILE_FBLOCK_EXCEPTION_HANDLER:
case COMPILE_FBLOCK_EXCEPTION_GROUP_HANDLER:
case COMPILE_FBLOCK_ASYNC_COMPREHENSION_GENERATOR:
+ case COMPILE_FBLOCK_INLINED_COMPREHENSION:
case COMPILE_FBLOCK_STOP_ITERATION:
return SUCCESS;
@@ -4685,8 +4686,11 @@ codegen_push_inlined_comprehension_locals(compiler *c,
location loc,
NEW_JUMP_TARGET_LABEL(c, cleanup);
state->cleanup = cleanup;
- // no need to push an fblock for this "virtual" try/finally; there
can't
- // be return/continue/break inside a comprehension
+ // Count against CO_MAXBLOCKS: SETUP_FINALLY consumes an except-stack
+ // slot even though return/continue/break cannot appear here.
+ RETURN_IF_ERROR(_PyCompile_PushFBlock(
+ c, loc, COMPILE_FBLOCK_INLINED_COMPREHENSION,
+ cleanup, NO_LABEL, NULL));
ADDOP_JUMP(c, loc, SETUP_FINALLY, cleanup);
}
return SUCCESS;
@@ -4732,6 +4736,8 @@ codegen_pop_inlined_comprehension_locals(compiler *c,
location loc,
{
if (state->pushed_locals) {
ADDOP(c, NO_LOCATION, POP_BLOCK);
+ _PyCompile_PopFBlock(c, COMPILE_FBLOCK_INLINED_COMPREHENSION,
+ state->cleanup);
NEW_JUMP_TARGET_LABEL(c, end);
ADDOP_JUMP(c, NO_LOCATION, JUMP_NO_INTERRUPT, end);
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