def extend(clself, other):
        clself._cfg_def.extend(other._cfg_def)
        for key, optdef in clself._cfg_def.options.iteritems():
            setattr(clself, key, optdef)
First element in a nested list
dataset/ETHPy150Open sassoftware/conary/conary/lib/cfg.py/_ConfigMeta.extend--crossover with--dataset/ETHPy150Open dask/dask/dask/array/core.py/deepfirst