collections and itertools

What you'll learn

• When to use Counter, defaultdict, and deque
• Iterator composition with itertools
• Memory-friendly processing patterns

Explanation

The standard library provides optimized building blocks for counting, grouping, queuing, and streaming computations without loading everything into memory.

Example

from collections import Counter

words = ["py", "py", "book", "docs"]
print(Counter(words).most_common(1))

Common mistakes

• Rebuilding utilities that already exist in collections
• Converting iterators to lists too early

Exercises

See Beyond the Basics Exercises.

Further reading

• https://docs.python.org/3/library/collections.html
• https://docs.python.org/3/library/itertools.html