You have written this shape of loop many times: start with an empty list, loop, append something each time.

numbers = [1, 2, 3, 4, 5]
squares = []
for n in numbers:
    squares.append(n * n)
print(squares)

Python has a shorter way to say exactly the same thing, called a list comprehension:

numbers = [1, 2, 3, 4, 5]
squares = [n * n for n in numbers]
print(squares)

Read it as "a list of n * n, for each n in numbers". The part before for is what goes into the new list; the for part is the same loop you'd write anyway.

words = ["apple", "banana", "cherry"]
print([w.upper() for w in words])
print([len(w) for w in words])
print([w[0] for w in words])
print([i * 10 for i in range(5)])