code: def replace_bases(self, old, new):
          '''Replaces all occurrences of 'old' with 'new' '''
          self.seq = self.seq.replace(old, newf replace_bases(self, old, new):
          '''Replaces all occurrences of 'old' with 'new' '''
          self.seq = self.seq.replace(old, new)
docs: Replaces all occurrences of 'old' with 'new'