input: Write a Python function to double the elements of a list.
  assert function([1, 2, 3, 4]) == [2, 4, 6, 8]
  assert function([0, 5, 10]) == [0, 10, 20]
  assert function([-1, -2, -3]) == [-2, -4, -6]
output: def function(lst):
      return [x * 2 for x in lst]