[3.12] gh-126618: fix repr(itertools.count(sys.maxsize)) (GH-127048) (#127510)

(cherry picked from commit 930ba0c)

Co-authored-by: Bénédikt Tran <[email protected]>

Author: skirpichev

Lib/test/test_itertools.py

@@ -623,6 +623,15 @@ def test_count(self):
         self.assertEqual(next(c), -8)
         self.assertEqual(repr(count(10.25)), 'count(10.25)')
         self.assertEqual(repr(count(10.0)), 'count(10.0)')
+
+        self.assertEqual(repr(count(maxsize)), f'count({maxsize})')
+        c = count(maxsize - 1)
+        self.assertEqual(repr(c), f'count({maxsize - 1})')
+        next(c)  # c is now at masize
+        self.assertEqual(repr(c), f'count({maxsize})')
+        next(c)
+        self.assertEqual(repr(c), f'count({maxsize + 1})')
+
         self.assertEqual(type(next(count(10.0))), float)
         for i in (-sys.maxsize-5, -sys.maxsize+5 ,-10, -1, 0, 10, sys.maxsize-5, sys.maxsize+5):
             # Test repr
@@ -703,6 +712,20 @@ def test_count_with_stride(self):
                 for proto in range(pickle.HIGHEST_PROTOCOL + 1):
                     self.pickletest(proto, count(i, j))
 
+        c = count(maxsize -2, 2)
+        self.assertEqual(repr(c), f'count({maxsize - 2}, 2)')
+        next(c)  # c is now at masize
+        self.assertEqual(repr(c), f'count({maxsize}, 2)')
+        next(c)
+        self.assertEqual(repr(c), f'count({maxsize + 2}, 2)')
+
+        c = count(maxsize + 1, -1)
+        self.assertEqual(repr(c), f'count({maxsize + 1}, -1)')
+        next(c)  # c is now at masize
+        self.assertEqual(repr(c), f'count({maxsize}, -1)')
+        next(c)
+        self.assertEqual(repr(c), f'count({maxsize - 1}, -1)')
+
     def test_cycle(self):
         self.assertEqual(take(10, cycle('abc')), list('abcabcabca'))
         self.assertEqual(list(cycle('')), [])

Misc/NEWS.d/next/Library/2024-11-20-08-54-11.gh-issue-126618.ef_53g.rst

@@ -0,0 +1,2 @@
+Fix the representation of :class:`itertools.count` objects when the count
+value is :data:`sys.maxsize`.

Modules/itertoolsmodule.c

@@ -3981,7 +3981,7 @@ typedef struct {
 
 fast_mode:  when cnt an integer < PY_SSIZE_T_MAX and no step is specified.
 
-    assert(cnt != PY_SSIZE_T_MAX && long_cnt == NULL && long_step==PyLong(1));
+    assert(long_cnt == NULL && long_step==PyLong(1));
     Advances with:  cnt += 1
     When count hits Y_SSIZE_T_MAX, switch to slow_mode.
 
@@ -4037,9 +4037,6 @@ itertools_count_impl(PyTypeObject *type, PyObject *long_cnt,
                 PyErr_Clear();
                 fast_mode = 0;
             }
-            else if (cnt == PY_SSIZE_T_MAX) {
-                fast_mode = 0;
-            }
         }
     } else {
         cnt = 0;
@@ -4071,7 +4068,7 @@ itertools_count_impl(PyTypeObject *type, PyObject *long_cnt,
     else
         cnt = PY_SSIZE_T_MAX;
 
-    assert((cnt != PY_SSIZE_T_MAX && long_cnt == NULL && fast_mode) ||
+    assert((long_cnt == NULL && fast_mode) ||
            (cnt == PY_SSIZE_T_MAX && long_cnt != NULL && !fast_mode));
     assert(!fast_mode ||
            (PyLong_Check(long_step) && PyLong_AS_LONG(long_step) == 1));
@@ -4143,7 +4140,7 @@ count_next(countobject *lz)
 static PyObject *
 count_repr(countobject *lz)
 {
-    if (lz->cnt != PY_SSIZE_T_MAX)
+    if (lz->long_cnt == NULL)
         return PyUnicode_FromFormat("%s(%zd)",
                                     _PyType_Name(Py_TYPE(lz)), lz->cnt);