Merge pull request #24028 from VadimLevin:dev/vlevin/fix-flann-python-bindings

Fix FLANN python bindings #24028

As a side-effect this patch improves reporting errors by FLANN `get_param`.

resolves #21642

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/flann/misc/python/pyopencv_flann.hpp

@@ -17,57 +17,89 @@ PyObject* pyopencv_from(const cvflann_flann_distance_t& value)
 template<>
 bool pyopencv_to(PyObject *o, cv::flann::IndexParams& p, const ArgInfo& info)
 {
-    CV_UNUSED(info);
-    bool ok = true;
-    PyObject* key = NULL;
-    PyObject* item = NULL;
-    Py_ssize_t pos = 0;
-
     if (!o || o == Py_None)
+    {
         return true;
+    }
 
-    if(PyDict_Check(o)) {
-        while(PyDict_Next(o, &pos, &key, &item))
+    if(!PyDict_Check(o))
+    {
+        failmsg("Argument '%s' is not a dictionary", info.name);
+        return false;
+    }
+
+    PyObject* key_obj = NULL;
+    PyObject* value_obj = NULL;
+    Py_ssize_t key_pos = 0;
+
+    while(PyDict_Next(o, &key_pos, &key_obj, &value_obj))
+    {
+        // get key
+        std::string key;
+        if (!getUnicodeString(key_obj, key))
         {
-            // get key
-            std::string k;
-            if (!getUnicodeString(key, k))
+            failmsg("Key at pos %lld is not a string", static_cast<int64_t>(key_pos));
+            return false;
+        }
+        // key_arg_info.name is bound to key lifetime
+        const ArgInfo key_arg_info(key.c_str(), false);
+
+        // get value
+        if (isBool(value_obj))
+        {
+            npy_bool npy_value = NPY_FALSE;
+            if (PyArray_BoolConverter(value_obj, &npy_value) >= 0)
             {
-                ok = false;
-                break;
+                p.setBool(key, npy_value == NPY_TRUE);
+                continue;
             }
-            // get value
-            if( !!PyBool_Check(item) )
+            PyErr_Clear();
+        }
+
+        int int_value = 0;
+        if (pyopencv_to(value_obj, int_value, key_arg_info))
+        {
+            if (key == "algorithm")
             {
-                p.setBool(k, item == Py_True);
-            }
-            else if( PyInt_Check(item) )
-            {
-                int value = (int)PyInt_AsLong(item);
-                if( strcmp(k.c_str(), "algorithm") == 0 )
-                    p.setAlgorithm(value);
-                else
-                    p.setInt(k, value);
-            }
-            else if( PyFloat_Check(item) )
-            {
-                double value = PyFloat_AsDouble(item);
-                p.setDouble(k, value);
+                p.setAlgorithm(int_value);
             }
             else
             {
-                std::string val_str;
-                if (!getUnicodeString(item, val_str))
-                {
-                    ok = false;
-                    break;
-                }
-                p.setString(k, val_str);
+                p.setInt(key, int_value);
             }
+            continue;
         }
-    }
+        PyErr_Clear();
 
-    return ok && !PyErr_Occurred();
+        double flt_value = 0.0;
+        if (pyopencv_to(value_obj, flt_value, key_arg_info))
+        {
+            if (key == "eps")
+            {
+                p.setFloat(key, static_cast<float>(flt_value));
+            }
+            else
+            {
+                p.setDouble(key, flt_value);
+            }
+            continue;
+        }
+        PyErr_Clear();
+
+        std::string str_value;
+        if (getUnicodeString(value_obj, str_value))
+        {
+            p.setString(key, str_value);
+            continue;
+        }
+        PyErr_Clear();
+        // All conversions are failed
+        failmsg("Failed to parse IndexParam with key '%s'. "
+                "Supported types: [bool, int, float, str]", key.c_str());
+        return false;
+
+    }
+    return true;
 }
 
 template<>

modules/flann/misc/python/test/test_flann_based_matcher.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import cv2
+import numpy as np
+
+from tests_common import NewOpenCVTests
+
+
+class FlannBasedMatcher(NewOpenCVTests):
+    def test_all_parameters_can_be_passed(self):
+        img1 = self.get_sample("samples/data/right01.jpg")
+        img2 = self.get_sample("samples/data/right02.jpg")
+
+        orb = cv2.ORB.create()
+
+        kp1, des1 = orb.detectAndCompute(img1, None)
+        kp2, des2 = orb.detectAndCompute(img2, None)
+        FLANN_INDEX_KDTREE = 1
+        index_param = dict(algorithm=FLANN_INDEX_KDTREE, trees=4)
+        search_param = dict(checks=32, sorted=True, eps=0.5,
+                            explore_all_trees=False)
+        matcher = cv2.FlannBasedMatcher(index_param, search_param)
+        matches = matcher.knnMatch(np.float32(des1), np.float32(des2), k=2)
+        self.assertGreater(len(matches), 0)
+
+
+if __name__ == '__main__':
+    NewOpenCVTests.bootstrap()