input: def sort_by_length(strings):
      """ Sorts the given list of strings by their length in ascending order.
      >>> sort_by_length(["cat", "dog", "apple", "banana"])
      ['cat', 'dog', 'apple', 'banana']
      """
      for i in range(len(strings) - 1):
          for j in range(i + 1, len(strings)):
              if len(strings[i]) > len(strings[j]):
                  strings[i], strings[j] = strings[j], strings[i]
      return strings
output:     for i in range(len(strings) - 1):
          for j in range(i + 1, len(strings)):
              if len(strings[i]) > len(strings[j]):
                  strings[i], strings[j] = strings[j], strings[i]
      return strings