houdiniEngine_setAssetInput
MEL command.// for parameter input
houdiniEngine_setAssetInput "test_null1.input[0].inputNodeId" {"pCube1"};
// for node input
houdiniEngine_setAssetInput "test_null1.houdiniAssetParm_objpath1__node" {"pCube1"};
From Python, you'd have to run the MEL commands with
maya.mel.eval
.