input: Write a function to convert ratings in a list of strings to a float.
  
  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(['1.0', '2.5', '3.75']) == [1.0, 2.5, 3.75]
  assert str_to_float(['0.5', '0.0', '5.5']) == [0.5, 0.0, 5.5]
  assert str_to_float(['1.1', '2.2', '3.3']) == [1.1, 2.2, 3.3]
  assert str_to_float([]) == []
output: def str_to_float(ratings):
      return [float(x) for x in ratings]