Time offset start and end of all rotoshapes

# Time offset start and end of all rotoshapes
import nuke.rotopaint as rp, _curvelib as cl

# Amount of frames to offset
time_offset = -200
t = nuke.frame()

# Get all Roto or RotoPaint nodes and loop through them
roto_nodes = [n for n in nuke.allNodes() if 'Roto' in n.Class()]
for roto_node in roto_nodes:
    curves_knob = roto_node["curves"]
    root_layer = curves_knob.rootLayer
    for e in root_layer:
        if isinstance(e, rp.Shape):
            print e.name
            lifetime_type = e.getAttributes().getCurve('ltt')
            range_from = e.getAttributes().getCurve('ltn')
            range_to = e.getAttributes().getCurve('ltm')

            for attr in [range_from, range_to]:
                # Skip shapes that have default values for start and end?
                # if lifetime_type.isDefault():
                #     print "skipping", e.name, "of", roto_node.name()
                #     continue
                attr_val = attr.evaluate(t)
                new_attr_val = attr_val + time_offset

                attr.addKey(t, new_attr_val)
                attr.removeAllKeys()