code: def _prepare_lines_(self, lines):
          
  
          result = []
          for line in lines:
              # Remove all whitespace 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.