If I have a dictionary in a dictionary, how can I ask for a key in constant time? 
For example:

```
def get_hobby(hobby):
    d = {'An' : {'Hobby': "Paintball", 'Age' : 22}, 'Jef' : {'Hobby' : "Football", 'Age': 24}, 'Jos' : {'Hobby': "Paintball", 'Age' : 46}}
assert get_hobby("Paintball") == ['An', 'Jos']

```

This doesn't work:

```
return d.keys[hobby]

```