input: Write a function to compare the lengths of two strings.
  assert compare_string_lengths('apple', 'banana')==-1
  assert compare_string_lengths('hello', 'world')==0
  assert compare_string_lengths('python', 'java')==1
output: def compare_string_lengths(str1, str2):
      if len(str1) < len(str2):
          return -1
      elif len(str1) > len(str2):
          return 1
      else:
          return 0