gh-135241: Changed the opcode of _pickle module to look for 00 and 01 specifically

Lib/test/test_pickle.py

@@ -376,6 +376,16 @@ class CUnpicklerTests(PyUnpicklerTests):
         bad_stack_errors = (pickle.UnpicklingError,)
         truncated_errors = (pickle.UnpicklingError,)
 
+        def test_issue135241(self):
+            # C implementation should check for hardcoded values 00 and 01
+            # when getting booleans from the INT opcode. Doing a str comparison
+            # to bypass truthy/falsy comparisons. These payloads should return
+            # 0, not False.
+            out1 = self.loads(b'I+0\n.')
+            self.assertTrue(str(out1) == str(0))
+            out2 = self.loads(b'I 0\n.')
+            self.assertTrue(str(out2) == str(0))
+
     class CPicklingErrorTests(PyPicklingErrorTests):
         pickler = _pickle.Pickler
 

Misc/NEWS.d/next/Library/2025-06-08-01-10-34.gh-issue-135241.5j18IW.rst

@@ -0,0 +1 @@
+The :code:`INT` opcode of the C accelerator ``_pickle`` module was updated to look only for "00" and "01" to push booleans onto the stack, aligning with the Python :mod:`pickle` module.

Modules/_pickle.c

@@ -5255,7 +5255,7 @@ load_int(PickleState *state, UnpicklerObject *self)
         }
     }
     else {
-        if (len == 3 && (x == 0 || x == 1)) {
+        if (len == 3 && s[0] == '0' && (s[1] == '0' || s[1] == '1')) {
             if ((value = PyBool_FromLong(x)) == NULL)
                 return -1;
         }