def nodeInputComesFromNode(self, dagNode, input):
        inputString = dagNode.inputValue(input.name)
        (connectedNode, connectedNodeOutput) = depends_data_packet.nodeAndOutputFromScenegraphLocationString(inputString, self)
        return (connectedNode, connectedNodeOutput)
Given a node and one of its inputs, return a tuple containing which 
dataset/ETHPy150Open andrew-gardner/dependsworkflow/depends/depends_dag.py/DAG.nodeInputComesFromNode