code: def append(self, element):
          '''
          Append a PileupElement to this Pileup. If an identical PileupElement is
          already part of this Pileup, do nothing.
          '''
          assert element.locus == self.locus, (
              "Element locus (%s) != Pileup locus (%s)"
              % (element.locus, self.locus))
          self.elements[element] = Nonf append(self, element):
          '''
          Append a PileupElement to this Pileup. If an identical PileupElement is
          already part of this Pileup, do nothing.
          '''
          assert element.locus == self.locus, (
              "Element locus (%s) != Pileup locus (%s)"
              % (element.locus, self.locus))
          self.elements[element] = None
docs: Append a PileupElement to this Pileup. If an identical PileupElement is
          already part of this Pileup, do nothing.