Daniel Arbuckle's Mastering Python

The defaultdict class

As an example of why that's interesting, consider this-Python's standard library contains a data structure class called defaultdict, which is like a dictionary except, when we try to look up a key that isn't already in the dictionary. It creates a new value and adds it to the dictionary, before returning it to the code that tried the lookup, as shown here:

How does the defaultdict class know how to create the default value?

The defaultdict class knows because we gave it class as a parameter when we created the defaultdict class. Thus, if we want a dictionary of list, we can give the defaultdict class the list class, as ...