ZeroIntensity · May 19, 2026 · May 18, 2026 · May 18, 2026 · May 18, 2026 · May 18, 2026
diff --git a/Include/internal/pycore_intrinsics.h b/Include/internal/pycore_intrinsics.h
@@ -18,8 +18,9 @@
 #define INTRINSIC_TYPEVARTUPLE                   9
 #define INTRINSIC_SUBSCRIPT_GENERIC             10
 #define INTRINSIC_TYPEALIAS                     11
+#define INTRINSIC_BUILD_FROZENSET               12
 
-#define MAX_INTRINSIC_1                         11
+#define MAX_INTRINSIC_1                         12
 
 
 /* Binary Functions: */

diff --git a/Include/internal/pycore_opcode_utils.h b/Include/internal/pycore_opcode_utils.h
@@ -80,7 +80,8 @@ extern "C" {
 #define CONSTANT_TRUE 9
 #define CONSTANT_FALSE 10
 #define CONSTANT_MINUS_ONE 11
-#define NUM_COMMON_CONSTANTS 12
+#define CONSTANT_BUILTIN_FROZENSET 12
+#define NUM_COMMON_CONSTANTS 13
 
 /* Values used in the oparg for RESUME */
 #define RESUME_AT_FUNC_START 0

diff --git a/Include/internal/pycore_setobject.h b/Include/internal/pycore_setobject.h
@@ -35,6 +35,9 @@ extern void _PySet_ClearInternal(PySetObject *so);
 
 PyAPI_FUNC(int) _PySet_AddTakeRef(PySetObject *so, PyObject *key);
 
+PyObject *
+_PyFrozenSet_NewAndSteal(PyObject *set);
+
 #ifdef __cplusplus
 }
 #endif

diff --git a/Lib/opcode.py b/Lib/opcode.py
@@ -44,7 +44,7 @@
                      builtins.set,
                      # Append-only — must match CONSTANT_* in
                      # Include/internal/pycore_opcode_utils.h.
-                     None, "", True, False, -1]
+                     None, "", True, False, -1, builtins.frozenset]
 _nb_ops = _opcode.get_nb_ops()
 
 hascompare = [opmap["COMPARE_OP"]]

diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
@@ -268,7 +268,10 @@ def f_list():
         def f_set():
             return set(2*x for x in [1,2,3])
 
-        funcs = [f_all, f_any, f_tuple, f_list, f_set]
+        def f_frozenset():
+            return frozenset(2*x for x in [1,2,3])
+
+        funcs = [f_all, f_any, f_tuple, f_list, f_set, f_frozenset]
 
         for f in funcs:
             # check that generator code object is not duplicated
@@ -278,35 +281,37 @@ def f_set():
 
         # check the overriding the builtins works
 
-        global all, any, tuple, list, set
-        saved = all, any, tuple, list, set
+        global all, any, tuple, list, set, frozenset
+        saved = all, any, tuple, list, set, frozenset
         try:
             all = lambda x : "all"
             any = lambda x : "any"
             tuple = lambda x : "tuple"
             list = lambda x : "list"
             set = lambda x : "set"
+            frozenset = lambda x : "frozenset"
 
             overridden_outputs = [f() for f in funcs]
         finally:
-            all, any, tuple, list, set = saved
+            all, any, tuple, list, set, frozenset = saved
 
-        self.assertEqual(overridden_outputs, ['all', 'any', 'tuple', 'list', 'set'])
+        self.assertEqual(overridden_outputs, ['all', 'any', 'tuple', 'list', 'set', 'frozenset'])
         # Now repeat, overriding the builtins module as well
-        saved = all, any, tuple, list, set
+        saved = all, any, tuple, list, set, frozenset
         try:
             builtins.all = all = lambda x : "all"
             builtins.any = any = lambda x : "any"
             builtins.tuple = tuple = lambda x : "tuple"
             builtins.list = list = lambda x : "list"
             builtins.set = set = lambda x : "set"
+            builtins.frozenset = frozenset = lambda x : "frozenset"
 
             overridden_outputs = [f() for f in funcs]
         finally:
-            all, any, tuple, list, set = saved
-            builtins.all, builtins.any, builtins.tuple, builtins.list, builtins.set = saved
+            all, any, tuple, list, set, frozenset = saved
+            builtins.all, builtins.any, builtins.tuple, builtins.list, builtins.set, builtins.frozenset = saved
 
-        self.assertEqual(overridden_outputs, ['all', 'any', 'tuple', 'list', 'set'])
+        self.assertEqual(overridden_outputs, ['all', 'any', 'tuple', 'list', 'set', 'frozenset'])
 
     def test_builtin_call_async_genexpr_no_crash(self):
         async def f_all():

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-05-18-17-16-51.gh-issue-150027.sJgLvd.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-05-18-17-16-51.gh-issue-150027.sJgLvd.rst
@@ -0,0 +1,2 @@
+Improve performance of :class:`frozenset` objects by avoiding copies during
+construction.
@@ -1545,6 +1545,16 @@ set_swap_bodies(PySetObject *a, PySetObject *b)
     FT_ATOMIC_STORE_PTR_RELEASE(b->table, b_table);
 }
 
+PyObject *
+_PyFrozenSet_NewAndSteal(PyObject *set)
+{
+    assert(set != NULL);
+    assert(PySet_CheckExact(set));
+    assert(_PyObject_IsUniquelyReferenced(set));
+    set->ob_type = &PyFrozenSet_Type;
+    return Py_NewRef(set);
+}
+
 /*[clinic input]
 @critical_section
 set.copy

@@ -3953,22 +3953,45 @@ maybe_optimize_function_call(compiler *c, expr_ty e, jump_target_label end)
 
     if (! (func->kind == Name_kind &&
            asdl_seq_LEN(args) == 1 &&
-           asdl_seq_LEN(kwds) == 0 &&
-           asdl_seq_GET(args, 0)->kind == GeneratorExp_kind))
+           asdl_seq_LEN(kwds) == 0))
     {
         return 0;
     }
 
-    expr_ty generator_exp = asdl_seq_GET(args, 0);
-    PySTEntryObject *generator_entry = _PySymtable_Lookup(SYMTABLE(c), (void *)generator_exp);
+    location loc = LOC(func);
+
+    expr_ty arg_expr = asdl_seq_GET(args, 0);
+
+    if (arg_expr->kind != GeneratorExp_kind) {
+        if (_PyUnicode_EqualToASCIIString(func->v.Name.id, "frozenset")
+            && (arg_expr->kind == Set_kind || arg_expr->kind == SetComp_kind)) {
+            NEW_JUMP_TARGET_LABEL(c, skip_optimization);
+
+            ADDOP_I(c, loc, COPY, 1);
+            ADDOP_I(c, loc, LOAD_COMMON_CONSTANT, CONSTANT_BUILTIN_FROZENSET);
+            ADDOP_COMPARE(c, loc, Is);
+            ADDOP_JUMP(c, loc, POP_JUMP_IF_FALSE, skip_optimization);
+            ADDOP(c, loc, POP_TOP);
+
+            VISIT(c, expr, arg_expr);
+            ADDOP_I(c, loc, CALL_INTRINSIC_1, INTRINSIC_BUILD_FROZENSET);
+
+            ADDOP_JUMP(c, loc, JUMP, end);
+
+            USE_LABEL(c, skip_optimization);
+            return 1;
+        }
+
+        return 0;
+    }
+
+    PySTEntryObject *generator_entry = _PySymtable_Lookup(SYMTABLE(c), (void *)arg_expr);
     if (generator_entry->ste_coroutine) {
         Py_DECREF(generator_entry);
         return 0;
     }
     Py_DECREF(generator_entry);
 
-    location loc = LOC(func);
-
     int optimized = 0;
     NEW_JUMP_TARGET_LABEL(c, skip_optimization);
 
@@ -3994,6 +4017,9 @@ maybe_optimize_function_call(compiler *c, expr_ty e, jump_target_label end)
     else if (_PyUnicode_EqualToASCIIString(func->v.Name.id, "set")) {
         const_oparg = CONSTANT_BUILTIN_SET;
     }
+    else if (_PyUnicode_EqualToASCIIString(func->v.Name.id, "frozenset")) {
+        const_oparg = CONSTANT_BUILTIN_FROZENSET;
+    }
     if (const_oparg != -1) {
         ADDOP_I(c, loc, COPY, 1); // the function
         ADDOP_I(c, loc, LOAD_COMMON_CONSTANT, const_oparg);
@@ -4003,10 +4029,10 @@ maybe_optimize_function_call(compiler *c, expr_ty e, jump_target_label end)
 
         if (const_oparg == CONSTANT_BUILTIN_TUPLE || const_oparg == CONSTANT_BUILTIN_LIST) {
             ADDOP_I(c, loc, BUILD_LIST, 0);
-        } else if (const_oparg == CONSTANT_BUILTIN_SET) {
+        } else if (const_oparg == CONSTANT_BUILTIN_SET || const_oparg == CONSTANT_BUILTIN_FROZENSET) {
             ADDOP_I(c, loc, BUILD_SET, 0);
         }
-        VISIT(c, expr, generator_exp);
+        VISIT(c, expr, arg_expr);
 
         NEW_JUMP_TARGET_LABEL(c, loop);
         NEW_JUMP_TARGET_LABEL(c, cleanup);
@@ -4017,7 +4043,7 @@ maybe_optimize_function_call(compiler *c, expr_ty e, jump_target_label end)
         if (const_oparg == CONSTANT_BUILTIN_TUPLE || const_oparg == CONSTANT_BUILTIN_LIST) {
             ADDOP_I(c, loc, LIST_APPEND, 3);
             ADDOP_JUMP(c, loc, JUMP, loop);
-        } else if (const_oparg == CONSTANT_BUILTIN_SET) {
+        } else if (const_oparg == CONSTANT_BUILTIN_SET || const_oparg == CONSTANT_BUILTIN_FROZENSET) {
             ADDOP_I(c, loc, SET_ADD, 3);
             ADDOP_JUMP(c, loc, JUMP, loop);
         }
@@ -4029,7 +4055,8 @@ maybe_optimize_function_call(compiler *c, expr_ty e, jump_target_label end)
         ADDOP(c, NO_LOCATION, POP_ITER);
         if (const_oparg != CONSTANT_BUILTIN_TUPLE &&
             const_oparg != CONSTANT_BUILTIN_LIST &&
-            const_oparg != CONSTANT_BUILTIN_SET) {
+            const_oparg != CONSTANT_BUILTIN_SET &&
+            const_oparg != CONSTANT_BUILTIN_FROZENSET) {
             ADDOP_LOAD_CONST(c, loc, initial_res == Py_True ? Py_False : Py_True);
         }
         ADDOP_JUMP(c, loc, JUMP, end);
@@ -4044,6 +4071,9 @@ maybe_optimize_function_call(compiler *c, expr_ty e, jump_target_label end)
         } else if (const_oparg == CONSTANT_BUILTIN_SET) {
             // result is already a set
         }
+        else if (const_oparg == CONSTANT_BUILTIN_FROZENSET) {
+            ADDOP_I(c, loc, CALL_INTRINSIC_1, INTRINSIC_BUILD_FROZENSET);
+        }
         else {
             ADDOP_LOAD_CONST(c, loc, initial_res);
         }

diff --git a/Python/intrinsics.c b/Python/intrinsics.c
@@ -9,6 +9,7 @@
 #include "pycore_intrinsics.h"    // INTRINSIC_PRINT
 #include "pycore_list.h"          // _PyList_AsTupleAndClear()
 #include "pycore_object.h"        // _PyObject_IsUniquelyReferenced()
+#include "pycore_setobject.h"     // _PyFrozenSet_NewAndSteal()
 #include "pycore_pyerrors.h"      // _PyErr_SetString()
 #include "pycore_runtime.h"       // _Py_ID()
 #include "pycore_typevarobject.h" // _Py_make_typevar()
@@ -207,6 +208,14 @@ make_typevar(PyThreadState* Py_UNUSED(ignored), PyObject *v)
     return _Py_make_typevar(v, NULL, NULL);
 }
 
+static PyObject *
+make_frozenset(PyThreadState* Py_UNUSED(ignored), PyObject *set)
+{
+    assert(PySet_CheckExact(set));
+    assert(_PyObject_IsUniquelyReferenced(set));
+    return _PyFrozenSet_NewAndSteal(set);
+}
+
 
 #define INTRINSIC_FUNC_ENTRY(N, F) \
     [N] = {F, #N},
@@ -225,6 +234,7 @@ _PyIntrinsics_UnaryFunctions[] = {
     INTRINSIC_FUNC_ENTRY(INTRINSIC_TYPEVARTUPLE, _Py_make_typevartuple)
     INTRINSIC_FUNC_ENTRY(INTRINSIC_SUBSCRIPT_GENERIC, _Py_subscript_generic)
     INTRINSIC_FUNC_ENTRY(INTRINSIC_TYPEALIAS, _Py_make_typealias)
+    INTRINSIC_FUNC_ENTRY(INTRINSIC_BUILD_FROZENSET, make_frozenset)
 };
 
 

@@ -892,6 +892,7 @@ pycore_init_builtins(PyThreadState *tstate)
     interp->common_consts[CONSTANT_FALSE] = Py_False;
     interp->common_consts[CONSTANT_MINUS_ONE] =
         (PyObject *)&_PyLong_SMALL_INTS[_PY_NSMALLNEGINTS - 1];
+    interp->common_consts[CONSTANT_BUILTIN_FROZENSET] = (PyObject *)&PyFrozenSet_Type;
     for (int i = 0; i < NUM_COMMON_CONSTANTS; i++) {
         assert(interp->common_consts[i] != NULL);
     }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Improve performance of :class:`frozenset` objects by avoiding copies during
		construction.