input: Write a function to convert the given list into a dictionary where each element of the list becomes a key and the corresponding value is a string representation of the key. If the list is empty, return an empty dictionary.
  assert list_to_dict([1, 2, 3, 4])=={1: 'one', 2: 'two', 3: 'three', 4: 'four'}
  assert list_to_dict([])=={}
output: def list_to_dict(lst):
      num_to_word = {1: 'one', 2: 'two', 3: 'three', 4: 'four'}
      return {key: num_to_word[key] for key in lst}