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', '2.3', '5.0', '0.5']) == [1.0, 2.3, 5.0, 0.5]
  assert str_to_float([]) == []
  assert str_to_float(['0.1', '0.2', '0.3', '0.4']) == [0.1, 0.2, 0.3, 0.4]
  assert str_to_float(['3.4', '3.4', '3.4', '3.4']) == [3.4, 3.4, 3.4, 3.4]
output: def str_to_float(ratings):
      return [float(x) for x in ratings]