code: def _prepare_lines(self, lines):
          
  
          result = list()
          for line in lines:
              # Remove all whitespace characters (e.g. spaces, line breaks, etc.)
              # from the start and end of the line.
              line = line.strip()
              # Replace all tabs with spaces.
              line = line.replace("\t", " ")
              # Replace all repeating spaces with a single space.
              while line.find("  ") > -1:
                  line = line.replace("  ", " ")
              result.append(line)
          return result
docs: Prepare the lines read from the text file before starting to process
          it.