how do I know what are the API's installed with opencv ?

edit

you can try:

>>> help(cv2.saliency)

but it's unlikely, that you have it, it's not installed by default, and you need to rebuild from src with opencv_contrib (and you would remember, if you'd done that..)

also you can look at:

>>> print(cv2.getBuildInformation())

there's a "to be build" section there, containing the list of modules, you can use.

also, please have a look at usage example in this question