nuke_lookingfor_first_by_type.py

import nuke

def get_nodes_by_type(node, types):
    array = []
    for inp in range(node.inputs()):
        inp_node = node.input(inp)
        if inp_node.Class() in types:
            array.append(inp_node)
        array.extend(get_nodes_by_type(inp_node, types))
    return array

last = nuke.selectedNode()

upstream = get_nodes_by_type(last, ['ColorCorrect','Grade'])
if not upstream:
    raise
first = upstream[-1]
print 'First node:', first.name()
# connect unptimult to first
unprim = nuke.nodes.Unpremult(inputs=[first.input(0)])
first.setInput(0, unprim)
# connect primult to last
downstream = last.dependent()
prim = nuke.nodes.Premult(inputs=[last])
if downstream:
    for d in downstream:
        d.setInput(d.inputs()-1, prim)