Python initialize empty dictionary with default values type

Question

I want to use a dictionary with string as key and set() as values.

How do I initialize an empty dictionary with a specific type as values?

I need it because I don't want to check everytime if the key is already in the dictionary and put an if to create the set instead of just using .add()

is it possible?

• David Buck: You appear to be looking for defaultdict
• AMC: Does this answer your question? Dictionaries and default values

Answer 1

Use defaultdict

from collections import defaultdict
mydict = defaultdict(set)
mydict["key"].add(5)

• Egret: Is it also possible to use just dict? i.e. mydict = dict(set)

Answer 2

You can also use setdefault() function on standard python dict to initialize keys not present.

setdefault() :

• returns default value passed if key is not present.
• returns None if key is not present and no default value passed
• returns value of key if key is present.

 x=dict()
 x.setdefault('a',set()).add(5)
 print(x) #{'a': {5}}
 x.setdefault('a',set()).add(6)
 print(x) #{'a': {5, 6}}