What are the differences between Counter and defaultdict in Python?

What are the differences between Counter and defaultdict in Python?

Both Counter and defaultdict are part of the collections module in Python, but they serve different purposes. Counter is specifically designed for counting hashable objects, while defaultdict provides a default value for non-existent keys.

Can you give me an example of how to use both?

Sure! For Counter, you can use it like this: from collections import Counter; counts = Counter(['a', 'b', 'a']) which will give you Counter({'a': 2, 'b': 1}). For defaultdict, you can do: from collections import defaultdict; d = defaultdict(int); d['key'] += 1 which initializes the key with a default value of 0.

When should I use Counter instead of defaultdict?

Use Counter when you need to count occurrences of items, as it provides methods like most_common(). Use defaultdict when you want to avoid key errors and provide default values for missing keys.

Are there any performance differences between them?

Yes, Counter can be more efficient for counting items since it's optimized for that purpose. defaultdict may have a slight overhead due to its default factory function.