input: Write a python function to generate a list of squares of numbers from 0 to n-1.
  assert generate_squares(10) == [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
  assert generate_squares(5) == [0, 1, 4, 9, 16]
  assert generate_squares(0) == []
output: def generate_squares(n):
      return [i**2 for i in range(n)]