retval return variable output and format on OpenCV2 python

I'm having some trouble understanding retval on some function in OpenCV2, some of it will only returning one variable and another returning up to four variable. I want to understand what type of data it returning, such as `BoundingRect`will returning x,y,width, height. and `cv2.useOptimized` will return 1 or 0 instead. how can i determine type of output (boolean, array, image, etc) from OpenCV manual? should i determine the output from it's C++ function?