I don't know 
but entering the command:
>>> dir()
into the Python interpreter gives a list of defined classes and variables.
Using the TAB key on one of the existing objects opens a list of possible completions, i.e. its methods/attributes.
I'm not sure this is what the OP is asking. I think s/he's referring to the API documentation rather than the API itself. Calling help(object) in the interpreter is a good start for help on an object.