When using python interface for NEURON, when I create a g=h.Graph() object in python, with g.addvar(...) to plot a variable, clicking Init & Run results in an empty Graph:
After creating the Graph() object, also add it to the global graphList. It will then be updated during run():
g = h.Graph()
g.addvar(...)
h.graphList[0].append(g)
h.run()