input: Write a function to convert a list of string ratings to a list of floating-point numbers. The function should return the list of floats corresponding to the input list of string ratings.
  def str_to_float(ratings):
      return [float(x) for x in ratings]
  
  assert str_to_float(['4.5', '3.0', '2.5', '4.0']) == [4.5, 3.0, 2.5, 4.0]
  assert str_to_float([]) == []
  assert str_to_float(['0.5', '1.0', '2.25']) == [0.5, 1.0, 2.25]
output: def str_to_float(ratings):
      return [float(x) for x in ratings]