Compound Data Structures

We can include containers in other containers to create compound data structures. For example, this dictionary maps keys to values that are also dictionaries!

elements = {"hydrogen": {"number": 1,
                         "weight": 1.00794,
                         "symbol": "H"},
              "helium": {"number": 2,
                         "weight": 4.002602,
                         "symbol": "He"}}

We can access elements in this nested dictionary like this.

helium = elements["helium"]  # get the helium dictionary
hydrogen_weight = elements["hydrogen"]["weight"]  # get hydrogen's weight

You can also add a new key to the element dictionary.

oxygen = {"number":8,"weight":15.999,"symbol":"O"}  # create a new oxygen dictionary 
elements["oxygen"] = oxygen  # assign 'oxygen' as a key to the elements dictionary
print('elements = ', elements)

Output is:
elements = {"hydrogen": {"number": 1, "weight": 1.00794, "symbol": 'H'}, "helium": {"number": 2, "weight": 4.002602, "symbol": "He"}, "oxygen": {"number": 8, "weight": 15.999, "symbol": "O"}}