Add a new item to a dictionary in Python

How do I add an item to an existing dictionary in Python? For example, given:

default_data = {
    'item1': 1,
    'item2': 2,
}

I want to add a new item such that:

default_data = default_data + {'item3': 3}

default_data['item3'] = 3

Easy as py.

Another possible solution:

default_data.update({'item3': 3})

which is nice if you want to insert multiple items at once.