input: Write a python function to create a dictionary with string lengths.
  assert length_dict(['apple', 'banana', 'orange']) == {'apple': 5, 'banana': 6, 'orange': 6}
  assert length_dict(['hello', 'world']) == {'hello': 5, 'world': 5}
  assert length_dict(['a', 'ab', 'abc', 'abcd']) == {'a': 1, 'ab': 2, 'abc': 3, 'abcd': 4}
output: def length_dict(strings):
      return {s: len(s) for s in strings}