python module's function pydoc

How to let vim be smart to judge what topic current is for help document.
for example:
import random
y = random.ran|dint(1, 6)
My cursor is at "|". When I press "K", it should open help for randint in module
random. But I do not know how to let a function know I'm is this module's
function.
Then let pydoc open "module.function"(random.randint) instead of not found.

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