Dictionary Comprehension

Same idea as a list comprehension, but it builds a dict — with a key: value pair on each side instead of a single expression.

squares = {
    x: x * x
    for x in range(5)
}

print(squares)   # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

{key: value for item in iterable}

JS has no direct equivalent this clean — you'd normally build an array of [key, value] pairs and convert it with Object.fromEntries():

const squares = Object.fromEntries(
  Array.from({ length: 5 }, (_, x) => [x, x * x]),
);

This is one of the cases where Python is noticeably more ergonomic than JS/TS. It also supports the same if filter as a list comprehension:

even_squares = {x: x * x for x in range(10) if x % 2 == 0}
# {0: 0, 2: 4, 4: 16, 6: 36, 8: 64}