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/package/cv2/_extra_py_code/__init__.py

@@ -0,0 +1,53 @@
+import sys
+import importlib
+
+__all__ = ['init']
+
+
+DEBUG = False
+if hasattr(sys, 'OpenCV_LOADER_DEBUG'):
+    DEBUG = True
+
+
+def _load_py_code(base, name):
+    try:
+        m = importlib.import_module(__name__ + name)
+    except ImportError:
+        return  # extension doesn't exist?
+
+    if DEBUG: print('OpenCV loader: added python code extension for: ' + name)
+
+    if hasattr(m, '__all__'):
+        export_members = { k : getattr(m, k) for k in m.__all__ }
+    else:
+        export_members = m.__dict__
+
+    for k, v in export_members.items():
+        if k.startswith('_'):  # skip internals
+            continue
+        if isinstance(v, type(sys)):  # don't bring modules
+            continue
+        if DEBUG: print('    symbol: {} = {}'.format(k, v))
+        setattr(sys.modules[base + name ], k, v)
+
+    del sys.modules[__name__ + name]
+
+
+# TODO: listdir
+def init(base):
+    _load_py_code(base, '.cv2')  # special case
+    prefix = base
+    prefix_len = len(prefix)
+
+    modules = [ m for m in sys.modules.keys() if m.startswith(prefix) ]
+    for m in modules:
+        m2 = m[prefix_len:]  # strip prefix
+        if len(m2) == 0:
+            continue
+        if m2.startswith('._'):  # skip internals
+            continue
+        if m2.startswith('.load_config_'):  # skip helper files
+            continue
+        _load_py_code(base, m2)
+
+    del sys.modules[__name__]