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gh-145749: Optimize named exception blocks #145983

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8da9704
gh-145749: Optimize named exception blocks
brijkapadia Mar 15, 2026
593ae3c
📜🤖 Added by blurb_it.
blurb-it[bot] Mar 15, 2026
cffaf20
Update 2026-03-15-18-54-06.gh-issue-145749.o1IQ5P.rst
brijkapadia Mar 15, 2026
d155803
Merge remote-tracking branch 'upstream' into named-exception
brijkapadia Jun 30, 2026
3a1efad
improve bytecode insertion
brijkapadia Jul 1, 2026
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8 changes: 3 additions & 5 deletions Lib/test/test_dis.py
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Original file line number Diff line number Diff line change
Expand Up @@ -470,24 +470,22 @@ def foo(a: int, b: str) -> str:

%4d LOAD_GLOBAL 0 (Exception)
CHECK_EXC_MATCH
POP_JUMP_IF_FALSE 24 (to L9)
POP_JUMP_IF_FALSE 22 (to L9)
L4: NOT_TAKEN
L5: STORE_FAST 0 (e)

%4d L6: LOAD_FAST 0 (e)
LOAD_ATTR 2 (__traceback__)
STORE_FAST 1 (tb)
L7: POP_EXCEPT
LOAD_COMMON_CONSTANT 7 (None)
PUSH_NULL
STORE_FAST 0 (e)
DELETE_FAST 0 (e)

%4d LOAD_FAST 1 (tb)
RETURN_VALUE

-- L8: LOAD_COMMON_CONSTANT 7 (None)
-- L8: PUSH_NULL
STORE_FAST 0 (e)
DELETE_FAST 0 (e)
RERAISE 1

%4d L9: RERAISE 0
Expand Down
8 changes: 4 additions & 4 deletions Lib/test/test_monitoring.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1955,8 +1955,8 @@ def func():
('branch', 'func', 4, 4),
('line', 'func', 5),
('line', 'meth', 1),
('jump', 'func', 5, '[offset=122]'),
('branch', 'func', '[offset=126]', '[offset=132]'),
('jump', 'func', 5, '[offset=118]'),
('branch', 'func', '[offset=122]', '[offset=128]'),
('line', 'get_events', 11)])

self.check_events(func, recorders = FLOW_AND_LINE_RECORDERS, expected = [
Expand All @@ -1970,8 +1970,8 @@ def func():
('line', 'func', 5),
('line', 'meth', 1),
('return', 'meth', None),
('jump', 'func', 5, '[offset=122]'),
('branch', 'func', '[offset=126]', '[offset=132]'),
('jump', 'func', 5, '[offset=118]'),
('branch', 'func', '[offset=122]', '[offset=128]'),
('return', 'func', None),
('line', 'get_events', 11)])

Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-03-15-18-54-06.gh-issue-145749.o1IQ5P.rst
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@@ -0,0 +1 @@
Named exception blocks are now faster as they no longer use a ``DELETE_FAST`` instruction.
64 changes: 44 additions & 20 deletions Python/codegen.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2331,6 +2331,46 @@ codegen_continue(compiler *c, location loc)
return SUCCESS;
}

static int
codegen_clear_exception_name(compiler *c, identifier name)
{
PyObject *mangled = _PyCompile_MaybeMangle(c, name);
if (mangled == NULL) {
return ERROR;
}

int scope = _PyST_GetScope(SYMTABLE_ENTRY(c), mangled);
if (scope == -1) {
Py_DECREF(mangled);
return ERROR;
}

_PyCompile_optype optype;
Py_ssize_t arg = 0;
if (_PyCompile_ResolveNameop(
c, mangled, scope, &optype, &arg) < 0) {
Py_DECREF(mangled);
return ERROR;
}

if (optype == COMPILE_OP_FAST) {
ADDOP(c, NO_LOCATION, PUSH_NULL);
ADDOP_N(c, NO_LOCATION, STORE_FAST_MAYBE_NULL, mangled, varnames);
Py_DECREF(mangled);
return SUCCESS;
}

Py_DECREF(mangled);

ADDOP_LOAD_CONST(c, NO_LOCATION, Py_None);
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, name, Store));
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, name, Del));

return SUCCESS;
}


/* Code generated for "try: <body> finally: <finalbody>" is as follows:

Expand Down Expand Up @@ -2574,22 +2614,14 @@ codegen_try_except(compiler *c, stmt_ty s)
ADDOP(c, NO_LOCATION, POP_BLOCK);
ADDOP(c, NO_LOCATION, POP_BLOCK);
ADDOP(c, NO_LOCATION, POP_EXCEPT);
ADDOP_LOAD_CONST(c, NO_LOCATION, Py_None);
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, handler->v.ExceptHandler.name, Store));
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, handler->v.ExceptHandler.name, Del));
codegen_clear_exception_name(c, handler->v.ExceptHandler.name);
ADDOP_JUMP(c, NO_LOCATION, JUMP_NO_INTERRUPT, end);

/* except: */
USE_LABEL(c, cleanup_end);

/* name = None; del name; # artificial */
ADDOP_LOAD_CONST(c, NO_LOCATION, Py_None);
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, handler->v.ExceptHandler.name, Store));
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, handler->v.ExceptHandler.name, Del));
codegen_clear_exception_name(c, handler->v.ExceptHandler.name);

ADDOP_I(c, NO_LOCATION, RERAISE, 1);
}
Expand Down Expand Up @@ -2771,11 +2803,7 @@ codegen_try_star_except(compiler *c, stmt_ty s)
/* name = None; del name; # artificial */
ADDOP(c, NO_LOCATION, POP_BLOCK);
if (handler->v.ExceptHandler.name) {
ADDOP_LOAD_CONST(c, NO_LOCATION, Py_None);
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, handler->v.ExceptHandler.name, Store));
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, handler->v.ExceptHandler.name, Del));
codegen_clear_exception_name(c, handler->v.ExceptHandler.name);
}
ADDOP_JUMP(c, NO_LOCATION, JUMP_NO_INTERRUPT, except);

Expand All @@ -2784,11 +2812,7 @@ codegen_try_star_except(compiler *c, stmt_ty s)

/* name = None; del name; # artificial */
if (handler->v.ExceptHandler.name) {
ADDOP_LOAD_CONST(c, NO_LOCATION, Py_None);
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, handler->v.ExceptHandler.name, Store));
RETURN_IF_ERROR(
codegen_nameop(c, NO_LOCATION, handler->v.ExceptHandler.name, Del));
codegen_clear_exception_name(c, handler->v.ExceptHandler.name);
}

/* add exception raised to the res list */
Expand Down
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