What is a defaultdict in Python?

What is a defaultdict in Python?

A defaultdict is a subclass of the built-in dict class in Python. It overrides one method to provide a default value for a nonexistent key.

How do I create a defaultdict?

You can create a defaultdict by importing it from the collections module and providing a default factory function. For example: from collections import defaultdict and then my_dict = defaultdict(int).

What happens if I access a key that doesn't exist?

If you access a key that doesn't exist in a defaultdict, it will automatically create that key with a default value returned by the factory function.

Can you give me an example of using defaultdict?

Sure! Here's an example: d = defaultdict(list); if you do d['a'].append(1), it creates a key 'a' with a default value of an empty list and appends 1 to it.