Merge pull request #19982 from TolyaTalamanov:at/new-python-operation-api

G-API: New python operations API

* Reimplement test using decorators

* Custom python operation API

* Remove wip status

* python: support Python code in bindings (through loader only)

* cleanup, skip tests for Python 2.x (not supported)

* python 2.x can't skip unittest modules

* Clean up

* Clean up

* Fix segfault python3.9

Co-authored-by: Alexander Alekhin <alexander.a.alekhin@gmail.com>

modules/python/python_loader.cmake

@@ -25,10 +25,12 @@ endif()
 set(PYTHON_LOADER_FILES
     "setup.py" "cv2/__init__.py"
     "cv2/load_config_py2.py" "cv2/load_config_py3.py"
+    "cv2/_extra_py_code/__init__.py"
 )
 foreach(fname ${PYTHON_LOADER_FILES})
   get_filename_component(__dir "${fname}" DIRECTORY)
-  file(COPY "${PYTHON_SOURCE_DIR}/package/${fname}" DESTINATION "${__loader_path}/${__dir}")
+  # avoid using of file(COPY) to rerun CMake on changes
+  configure_file("${PYTHON_SOURCE_DIR}/package/${fname}" "${__loader_path}/${fname}" COPYONLY)
   if(fname STREQUAL "setup.py")
     if(OPENCV_PYTHON_SETUP_PY_INSTALL_PATH)
       install(FILES "${PYTHON_SOURCE_DIR}/package/${fname}" DESTINATION "${OPENCV_PYTHON_SETUP_PY_INSTALL_PATH}" COMPONENT python)