def setdefault(self, key, default=None):
        if key in self:
            return self[key]
        self[key] = default
        return default
od.setdefault(k[,d]) -> od.get(k,d), also set od[k]=d if k not in od
dataset/ETHPy150Open PythonCharmers/python-future/docs/3rd-party-py3k-compat-code/pandas_py3k.py/_OrderedDict.setdefault