gh-61103: use PEP 3118 codes in the ctypes

Doc/whatsnew/3.15.rst

@@ -879,6 +879,15 @@ contextlib
   (Contributed by Alex Grönholm & Gregory P. Smith in :gh:`125862`.)
 
 
+ctypes
+------
+
+* Change the ``format`` field of exported buffers from ``F``, ``D`` and ``G``
+  to ``Zf``, ``Zd`` and ``Zg``, respectively, for compatibility with
+  the :pep:`3118` and NumPy.
+  (Contributed by Sergey B Kirpichev in :gh:`149344`.)
+
+
 dataclasses
 -----------
 

Lib/test/test_ctypes/test_pep3118.py

@@ -1,3 +1,4 @@
+import ctypes
 import re
 import sys
 import unittest
@@ -231,6 +232,14 @@ class Complete(Structure):
 
     ]
 
+if hasattr(ctypes, 'c_float_complex'):
+    c_float_complex = ctypes.c_float_complex
+    c_double_complex = ctypes.c_double_complex
+    c_longdouble_complex = ctypes.c_longdouble_complex
+    native_types.extend([(c_float_complex * 4,      "<Zf", (4,), c_float_complex),
+                         (c_double_complex * 4,     "<Zd", (4,), c_double_complex),
+                         (c_longdouble_complex * 4, "<Zg", (4,), c_longdouble_complex)])
+
 
 class BEPoint(BigEndianStructure):
     _fields_ = [("x", c_long), ("y", c_long)]

Misc/NEWS.d/next/Library/2026-05-04-05-08-17.gh-issue-61103.mONh4V.rst

@@ -0,0 +1,2 @@
+Use :pep:`3118` type codes for the buffer protocol support of complex types
+in the :mod:`ctypes`.  Patch by Sergey B Kirpichev.

Modules/_ctypes/_ctypes.c

@@ -305,6 +305,34 @@ _ctypes_alloc_format_string_for_type(char code, int big_endian)
 #else
 # error SIZEOF__BOOL has an unexpected value
 #endif /* SIZEOF__BOOL */
+#if defined(_Py_FFI_SUPPORT_C_COMPLEX)
+    /* complex types */
+    case 'F':
+    case 'D':
+    case 'G':
+    {
+        result = PyMem_Malloc(4);
+        if (result == NULL) {
+            PyErr_NoMemory();
+            return NULL;
+        }
+
+        result[0] = big_endian ? '>' : '<';
+        result[1] = 'Z';
+        switch (code) {
+        case 'F':
+            result[2] = 'f';
+            break;
+        case 'D':
+            result[2] = 'd';
+            break;
+        default:
+            result[2] = 'g';
+        }
+        result[3] = '\0';
+        return result;
+    }
+#endif
     default:
         /* The standard-size code is the same as the ctypes one */
         pep_code = code;