def listNamespaces_old():
    try:
        return [ cmds.file( x, q=1, namespace=1) for x in cmds.file( q=1, reference=1)  ]
    except:
        return []
New sequence with elements in either sequence or other, but not both.
dataset/ETHPy150Open CountZer0/PipelineConstructionSet/python/maya/site-packages/pymel-1.0.3/pymel/core/system.py/listNamespaces_old--crossover with--dataset/ETHPy150Open EntilZha/PyFunctional/functional/pipeline.py/Sequence.symmetric_difference