collections. Use of defaultdict()

This function and the common dict The difference between them is , It can assign a default variable to the new key ：

As shown below , Let's customize a class , In this case, it is passed as a variable to defaultdict, Then d It is equivalent to an initialized dictionary

At this point, we give this dictionary a new key as follows ： You can see this new key Of value This is the class we set up ourselves .

 

We call the methods of this class , give the result as follows