test_set_type_updates_format

Author: youknowone

Lib/test/test_ctypes/test_incomplete.py

@@ -1,6 +1,6 @@
 import ctypes
 import unittest
-from ctypes import Structure, POINTER, pointer, c_char_p
+from ctypes import Structure, POINTER, pointer, c_char_p, c_int
 
 # String-based "incomplete pointers" were implemented in ctypes 0.6.3 (2003, when
 # ctypes was an external project). They made obsolete by the current
@@ -50,6 +50,29 @@ class cell(Structure):
         lpcell.set_type(cell)
         self.assertIs(POINTER(cell), lpcell)
 
+    def test_set_type_updates_format(self):
+        # gh-142966: set_type should update StgInfo.format
+        # to match the element type's format
+        with self.assertWarns(DeprecationWarning):
+            lp = POINTER("node")
+
+        class node(Structure):
+            _fields_ = [("value", c_int)]
+
+        # Get the expected format before set_type
+        node_format = memoryview(node()).format
+        expected_format = "&" + node_format
+
+        lp.set_type(node)
+
+        # Create instance to check format via memoryview
+        n = node(42)
+        p = lp(n)
+        actual_format = memoryview(p).format
+
+        # After set_type, the pointer's format should be "&<element_format>"
+        self.assertEqual(actual_format, expected_format)
+
 
 if __name__ == '__main__':
     unittest.main()