How do I merge two dictionaries in a single expression in Python?

I want to merge two dictionaries into a new dictionary.

x = {'a': 1, 'b': 2}y = {'b': 3, 'c': 4}z = merge(x, y)>>> z{'a': 1, 'b': 3, 'c': 4}

Whenever a key k is present in both dictionaries, only the value y[k] should be kept.