Pandas Dataframe add column with dict value

Question

I am quite new in the data analytics/science field and have a question regarding adding a column to my pandas dataframe from a dict.

My datafram looks something like this:

data = [['LON', 9], ['PAR', 2.2], ['NYC', 8.5], ['PEK', 21.4]]

cities = pd.DataFrame(data, columns=['Code', 'Population'])

code	poulation
LON	9.0
PAR	2.2
NYC	8.5
PEK	21.4

I hava a dict with the mapping of code to city name:

codes = {'LON': 'LONDON', 'PAR': 'PARIS', 'NYC': 'NEW YORK CITY', 'PEK': 'PEKING'}

And I wanna add now a column 'city' to the dataframe so it looks like this:

code	poulation	city
LON	9.0	LONDON
PAR	2.2	PARIS
NYC	8.5	NEW YORK CITY
PEK	21.4	PEKING

What is the best way to do this? In face I am dealing with a realy large dataset, so shoud be efficient as possible.

Thank you very much for your answer.