Lesson 2 — Dict & set comprehensions

Build maps fast

A dict comprehension works like a list comprehension, but builds a dictionary. Use curly braces instead of square ones and write key: value before the for. Each turn of the loop adds one key with its value.

nums = [1, 2, 3]
squares = {n: n * n for n in nums}
print(squares)  # {1: 1, 2: 4, 3: 9}

Why it matters: turning a list into a lookup table (id to user, word to count) is one of the most common data tasks.