gh-157495: Implement Py_MIN() and Py_MAX() using typeof()

If typeof() is available, implement Py_MIN(), Py_MAX() and Py_ABS()
using typeof() and statement expression to only evaluate each
argument once.

Test also these macros in test_cext and test_cppext to test different
compiler flags and test the limited C API.

Author: vstinner

Include/pymacro.h

@@ -107,15 +107,35 @@
 #   endif
 #endif
 
+#if defined(_Py_TYPEOF) && !defined(__cplusplus)
+   // Implement Py_MIN(), Py_MAX() and Py_ABS() using _Py_TYPEOF() and
+   // statement expression to only evaluate each argument only once.
+   // It cannot be used in C++: ISO C++ forbids braced-groups within
+   // expressions.
 
-/* Minimum value between x and y */
-#define Py_MIN(x, y) (((x) > (y)) ? (y) : (x))
-
-/* Maximum value between x and y */
-#define Py_MAX(x, y) (((x) > (y)) ? (x) : (y))
+   /* Minimum value between x and y */
+#  define Py_MIN(x, y) \
+       ({ _Py_TYPEOF (x) _x = (x); \
+          _Py_TYPEOF (y) _y = (y); \
+          _x < _y ? _x : _y; })
+   /* Maximum value between x and y */
+#  define Py_MAX(x, y) \
+       ({ _Py_TYPEOF (x) _x = (x); \
+          _Py_TYPEOF (y) _y = (y); \
+          _x > _y ? _x : _y; })
+   /* Absolute value of the number x */
+#  define Py_ABS(x) \
+       ({ _Py_TYPEOF (x) _x = (x); \
+          _x < 0 ? -_x : _x; })
+#else
+   /* Minimum value between x and y */
+#  define Py_MIN(x, y) (((x) > (y)) ? (y) : (x))
+   /* Maximum value between x and y */
+#  define Py_MAX(x, y) (((x) > (y)) ? (x) : (y))
+   /* Absolute value of the number x */
+#  define Py_ABS(x) ((x) < 0 ? -(x) : (x))
+#endif
 
-/* Absolute value of the number x */
-#define Py_ABS(x) ((x) < 0 ? -(x) : (x))
 /* Safer implementation that avoids an undefined behavior for the minimal
    value of the signed integer type if its absolute value is larger than
    the maximal value of the signed integer type (in the two's complement

Lib/test/test_cext/extension.c

@@ -91,10 +91,15 @@ _testcext_exec(PyObject *module)
     if (!result) return -1;
     Py_DECREF(result);
 
-    // test Py_BUILD_ASSERT() and Py_BUILD_ASSERT_EXPR()
+    // Test Py_BUILD_ASSERT() and Py_BUILD_ASSERT_EXPR()
     Py_BUILD_ASSERT(sizeof(int) == sizeof(unsigned int));
     assert(Py_BUILD_ASSERT_EXPR(sizeof(int) == sizeof(unsigned int)) == 0);
 
+    // Test Py_MIN(), Py_MAX(), Py_ABS()
+    assert(Py_MIN(5, 11) == 5);
+    assert(Py_MAX(5, 11) == 11);
+    assert(Py_ABS(-5) == 5);
+
     // Test Py_CLEAR(): use typeof()/__typeof__() if available, or memcpy()
     obj = Py_None;
     Py_CLEAR(obj);

Lib/test/test_cppext/extension.cpp

@@ -294,6 +294,11 @@ _testcppext_exec(PyObject *module)
     Py_BUILD_ASSERT(sizeof(int) == sizeof(unsigned int));
     assert(Py_BUILD_ASSERT_EXPR(sizeof(int) == sizeof(unsigned int)) == 0);
 
+    // Test Py_MIN(), Py_MAX(), Py_ABS()
+    assert(Py_MIN(5, 11) == 5);
+    assert(Py_MAX(5, 11) == 11);
+    assert(Py_ABS(-5) == 5);
+
     // Test Py_CLEAR(): use typeof()/__typeof__() if available, or memcpy()
     PyObject *obj = Py_None;
     Py_CLEAR(obj);

Misc/NEWS.d/next/C_API/2026-09-14-16-10-23.gh-issue-157495.LzMLtE.rst

@@ -0,0 +1,3 @@
+If ``typeof()`` is available, implement :c:macro:`Py_MIN`, :c:macro:`Py_MAX`
+and :c:macro:`Py_ABS` using ``typeof()`` and statement expression to only
+evaluate each argument once. Patch by Victor Stinner.

Modules/_testcapimodule.c

@@ -2045,12 +2045,21 @@ test_macros(PyObject *self, PyObject *Py_UNUSED(args))
     static_assert(1 == 1, "bug");
     Py_BUILD_ASSERT(1 == 1);
 
-
     // Py_MIN(), Py_MAX(), Py_ABS()
     assert(Py_MIN(5, 11) == 5);
     assert(Py_MAX(5, 11) == 11);
     assert(Py_ABS(-5) == 5);
 
+#ifdef _Py_TYPEOF
+    // When _Py_TYPEOF() is available, arguments are only evaluated once
+    int x = 5, y = 11;
+    assert(Py_MIN(++x, ++y) == 6);
+    x = 5; y = 11;
+    assert(Py_MAX(++x, ++y) == 12);
+    x = -5;
+    assert(Py_ABS(--x) == 6);
+#endif
+
     // Py_STRINGIFY()
     assert(strcmp(Py_STRINGIFY(123), "123") == 0);