c++ - Connect QML signal to C++11 lambda slot (Qt 5) - Stack Overflow
Warning: While it is possible to use C++ to access and manipulate QML objects deep into the object tree, we recommend that you do not take this approach outside of application testing and prototyping.
python - Is the PySide Slot Decorator Necessary? - Stack Overflow
If you don't use the slot decorator, the signal connection mechanism has to manually work out all the type conversions to map from the underlying C++ function signatures to the Python functions.
Calling C++ slot from Qml signal
Thus, you can access the object that was loaded into the context of the QML engine, call its slot, and process the signal from this object.