old_contents: class DNA(object):
      thymidine = 'T'
      uracil = 'U'
  
      def __init__(self, strand):
          self.strand = strand
  
      def to_rna(self):
          return self.strand.replace(
              self.thymidine,
              self.uracil
          )
  
new_contents: from string import maketrans
  
  class DNA(object):
      rna_translation = maketrans('AGCT', 'AGCU')
  
      def __init__(self, strand):
          self.strand = strand
  
      def to_rna(self):
          return self.strand.translate(self.rna_translation)
  
subject: use better method for translation in example