Share 'DataTree,List,Item access from grasshopper-python'

Hi,   I'm using the python component for grasshopper, and have wondered to access to the data structure which grasshopper consists.    using a=ghdoc seems to be efficient for output, but I can't get the right data structure as input.   anything will help.   I'm sure that I'm using the latest component(v0.4.1.1)