import maya.cmds as cmds

def create_nurbs_curve_set(set_name):
    if not cmds.objExists(set_name):
        cmds.sets(name=set_name, empty=True)

def add_nurbs_curves_to_set(set_name):
    curve_transforms = [cmds.listRelatives(i, p=1, type='transform', fullPath=True)[0] for i in cmds.ls(type='nurbsCurve', o=1, r=1, ni=1)]
    for c in curve_transforms:
        cmds.sets(c, add=set_name)

def main():
    set_name = "Sets"
    create_nurbs_curve_set(set_name)
    add_nurbs_curves_to_set(set_name)

if __name__ == "__main__":
    main()