fix: preserve NumPY writeable flag in output arguments

modules/python/src2/cv2_convert.cpp

@@ -101,6 +101,13 @@ bool pyopencv_to(PyObject* o, Mat& m, const ArgInfo& info)
 
     PyArrayObject* oarr = (PyArrayObject*) o;
 
+    if (info.outputarg && !PyArray_ISWRITEABLE(oarr))
+    {
+        failmsg("%s marked as output argument, but provided NumPy array "
+                "marked as readonly", info.name);
+        return false;
+    }
+
     bool needcopy = false, needcast = false;
     int typenum = PyArray_TYPE(oarr), new_typenum = typenum;
     int type = typenum == NPY_UBYTE ? CV_8U :

modules/python/test/test_misc.py

@@ -232,6 +232,12 @@ class Arguments(NewOpenCVTests):
                     Exception, msg, cv.utils.dumpInputArray, test_array
                 )
 
+    def test_numpy_writeable_flag_is_preserved(self):
+        array = np.zeros((10, 10, 1), dtype=np.uint8)
+        array.setflags(write=False)
+        with self.assertRaises(Exception):
+            cv.rectangle(array, (0, 0), (5, 5), (255), 2)
+
     def test_20968(self):
         pixel = np.uint8([[[40, 50, 200]]])
         _ = cv.cvtColor(pixel, cv.COLOR_RGB2BGR)  # should not raise exception