I have a dictionary:

```
{'key1':1, 'key2':2, 'key3':3}

```

I need to pass a sub-set of that dictionary to third-party code. It only wants a dictionary containing keys `['key1', 'key2', 'key99']` and if it gets another key (eg `'key3'`), it explodes in a nasty mess. The code in question is out of my control so I'm left in a position where I have to clean my dictionary.

What's the best, way to limit a dictionary to a set of keys?

Given the example dictionary and allowed keys above, I want:

```
{'key1':1, 'key2':2}

```