37 – Multi-dictionary

37 – Multi-dictionary#

You can create a multi-dictionary in Python with collections.defaultdict and the built-in list with multidict = collections.defaultdict(list):

from collections import defaultdict

multidict = defaultdict(list)

This creates a dictionary that maps every single key to an empty list by default, which is why you use defaultdict in the first place:

print(multidict["SW"])  # []
print(multidict["LotR"])  # []

Then, when you want to “add a value to a key”, you instead append to the list mapped to by that key:

multidict["SW"].append("Han Solo")
multidict["SW"].append("R2D2")
print(multidict["SW"])  # ['Han Solo', 'R2D2']

However, it goes without saying that this is “cheating”: the dictionary still maps each key to a single list. You’re just leveraging the fact that lists can store multiple values in them to.