From 92b6cbbfa1ae5b224441fd50ecbfb58f7b3a6b6f Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 4 May 2026 05:08:35 +0300
Subject: [PATCH 1/3] gh-61103: use PEP 3118 codes in the ctypes

This change only buffer protocol support for complex types,
`_type_` properties aren't affected.
---
 Lib/test/test_ctypes/test_pep3118.py          |  9 +++++++
 ...6-05-04-05-08-17.gh-issue-61103.mONh4V.rst |  2 ++
 Modules/_ctypes/_ctypes.c                     | 25 +++++++++++++++++--
 3 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2026-05-04-05-08-17.gh-issue-61103.mONh4V.rst

diff --git a/Lib/test/test_ctypes/test_pep3118.py b/Lib/test/test_ctypes/test_pep3118.py
index 11a0744f5a8e36..9740e0c77b5c87 100644
--- a/Lib/test/test_ctypes/test_pep3118.py
+++ b/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)]
diff --git a/Misc/NEWS.d/next/Library/2026-05-04-05-08-17.gh-issue-61103.mONh4V.rst b/Misc/NEWS.d/next/Library/2026-05-04-05-08-17.gh-issue-61103.mONh4V.rst
new file mode 100644
index 00000000000000..cba4f1097af076
--- /dev/null
+++ b/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.
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 5325321efe75cd..7146fa70c007a0 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -311,7 +311,7 @@ _ctypes_alloc_format_string_for_type(char code, int big_endian)
         break;
     }
 
-    result = PyMem_Malloc(3);
+    result = PyMem_Malloc(4);
     if (result == NULL) {
         PyErr_NoMemory();
         return NULL;
@@ -320,6 +320,7 @@ _ctypes_alloc_format_string_for_type(char code, int big_endian)
     result[0] = big_endian ? '>' : '<';
     result[1] = pep_code;
     result[2] = '\0';
+    result[3] = '\0';
     return result;
 }
 
@@ -3120,7 +3121,27 @@ PyCData_NewGetBuffer(PyObject *myself, Py_buffer *view, int flags)
     view->len = self->b_size;
     view->readonly = 0;
     /* use default format character if not set */
-    view->format = info->format ? info->format : "B";
+    if (!info->format) {
+        view->format = "B";
+    }
+    else {
+        view->format = info->format;
+        if (view->format[1] == 'F') {
+            view->format[1] = 'Z';
+            view->format[2] = 'f';
+            view->format[3] = '\0';
+        }
+        if (view->format[1] == 'D') {
+            view->format[1] = 'Z';
+            view->format[2] = 'd';
+            view->format[3] = '\0';
+        }
+        if (view->format[1] == 'G') {
+            view->format[1] = 'Z';
+            view->format[2] = 'g';
+            view->format[3] = '\0';
+        }
+    }
     view->ndim = info->ndim;
     view->shape = info->shape;
     view->itemsize = item_info->size;

From 9528d510bb523d5ddb8baa04eb4170e45a909a08 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 4 May 2026 06:06:57 +0300
Subject: [PATCH 2/3] +correct

---
 Modules/_ctypes/_ctypes.c | 53 ++++++++++++++++++++++-----------------
 1 file changed, 30 insertions(+), 23 deletions(-)

diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 7146fa70c007a0..4a5b4f61712727 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -305,13 +305,41 @@ _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;
         break;
     }
 
-    result = PyMem_Malloc(4);
+    result = PyMem_Malloc(3);
     if (result == NULL) {
         PyErr_NoMemory();
         return NULL;
@@ -320,7 +348,6 @@ _ctypes_alloc_format_string_for_type(char code, int big_endian)
     result[0] = big_endian ? '>' : '<';
     result[1] = pep_code;
     result[2] = '\0';
-    result[3] = '\0';
     return result;
 }
 
@@ -3121,27 +3148,7 @@ PyCData_NewGetBuffer(PyObject *myself, Py_buffer *view, int flags)
     view->len = self->b_size;
     view->readonly = 0;
     /* use default format character if not set */
-    if (!info->format) {
-        view->format = "B";
-    }
-    else {
-        view->format = info->format;
-        if (view->format[1] == 'F') {
-            view->format[1] = 'Z';
-            view->format[2] = 'f';
-            view->format[3] = '\0';
-        }
-        if (view->format[1] == 'D') {
-            view->format[1] = 'Z';
-            view->format[2] = 'd';
-            view->format[3] = '\0';
-        }
-        if (view->format[1] == 'G') {
-            view->format[1] = 'Z';
-            view->format[2] = 'g';
-            view->format[3] = '\0';
-        }
-    }
+    view->format = info->format ? info->format : "B";
     view->ndim = info->ndim;
     view->shape = info->shape;
     view->itemsize = item_info->size;

From 7aa47c369aeaa8e8fcf39453fce9ac6f45a22b73 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 4 May 2026 16:01:55 +0300
Subject: [PATCH 3/3] add news

---
 Doc/whatsnew/3.15.rst | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Doc/whatsnew/3.15.rst b/Doc/whatsnew/3.15.rst
index 586a1306d83c4c..6fff4c62a8b529 100644
--- a/Doc/whatsnew/3.15.rst
+++ b/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
 -----------