From my ipython shell, I see a method setdefault in os.environ but it is not documented. <http://docs.python.org/library/os.html#os.environ>. Is it documented somewhere else?

```
def setdefault(self, key, failobj=None):
    if key not in self:
        self[key] = failobj
    return self[key]

```

Can I use this function or write a wrapper for those lines?