MAYA: quick and dirty way to save/load shading states between render layers

shading_state.py

import maya.cmds as mc

if not hasattr(mc, "CLIPBOARD"):
    mc.CLIPBOARD = dict()


def get_shading(node):
    rval = dict()

    type_ = cmds.nodeType(node)
    if type_ != "transform":
        return rval

    for shape in cmds.listRelatives(node, s=True, f=True) or []:
        sg = cmds.listConnections(shape, t="shadingEngine") or []
        if len(sg):
            rval[shape] = sg[0]
    return rval


def save_shading_state(nodes=None):
    mc.CLIPBOARD.clear()
    nodes = nodes or cmds.ls(sl=True, l=True)
    
    for node in nodes:
        mc.CLIPBOARD.update(get_shading(node))


def load_shading_state():
    for k, v in mc.CLIPBOARD.iteritems():
        cmds.sets(k, edit=True, forceElement=v)

save_shading_state()
load_shading_state()