Dictionaries have a get() method
Dictionaries have a 'get()' method. If you do d['key'] and key isn't there, you get an exception. If you do d.get('key'), you get back None if 'key' isn't there. You can add a second argument to get that item back instead of None, eg: d.get('key', 0).
It's great for things like adding up numbers:
sum[value] = sum.get(value, 0) + 1
