Higher-order: filter then map

A higher-order function takes another function as an argument. Two classics are filter (keep items that pass a test) and map (transform every item):

nums = [1, -2, 3]
filter(lambda n: n > 0, nums)   # keeps 1 and 3
map(lambda n: n * n, nums)      # squares each item
list(...)                       # both are lazy — wrap in list() to see values

Chaining them is a clean pipeline: first filter the data, then map a transform over what survives.

Your task

Write positives_squared(nums) that keeps only the strictly positive numbers, then squares them, using filter() and map(). Return a list.

positives_squared([-2, -1, 0, 3, 4])   # [9, 16]
positives_squared([1, 2, 3])           # [1, 4, 9]
positives_squared([-5])                # []

Hint: kept = filter(lambda n: n > 0, nums), then list(map(lambda n: n * n, kept)).