python Dictionaries get method use

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 grate for adding up numbers:

sum[value] = sum.get(value, 0) + 1