docs: def _calculateCoverageMasks(proteindb, peptidedb):
          """Calcualte the sequence coverage masks for all proteindb elements.
          Private method used by :class:`ProteinDatabase`.
  
          A coverage mask is a numpy boolean array with the length of the protein
          sequence. Each protein position that has been covered in at least one
          peptide is set to True. Coverage masks are calculated for unique and for
          shared peptides. Peptides are matched to proteins according to positions
          derived by the digestion of the FASTA file.
  
          Alternatively peptides could also be matched to proteins just by
          sequence as it is done in :func:`pyteomics.parser.coverage`, but this is
          not the case here.
  
          :param proteindb: a dictionary containing :class:`ProteinSequence`
              entries, for example ``ProteinDatabase.proteins``
          :param proteindb: a dictionary containing :class:`PeptideSequence`
              entries, for example ``ProteinDatabase.peptides``
  
          Sets two attributes for each ``ProteinSequence`` entry:
              ``.coverageMaskUnique`` = coverage mask of unique peptides
              ``.coverageMaskShared`` = coverage mask of shared peptides
          """
          for proteinId, proteinEntry in viewitems(proteindb):
              coverageMaskUnique = numpy.zeros(proteinEntry.length(), dtype='bool')
              for peptide in proteinEntry.uniquePeptides:
                  startPos, endPos = peptidedb[peptide].proteinPositions[proteinId]
                  coverageMaskUnique[startPos-1:endPos] = True
              coverageMaskShared = numpy.zeros(proteinEntry.length(), dtype='bool')
              for peptide in proteinEntry.sharedPeptides:
                  startPos, endPos = peptidedb[peptide].proteinPositions[proteinId]
                  coverageMaskShared[startPos-1:endPos] = True
              setattr(proteinEntry, 'coverageMaskUnique', coverageMaskUnique)
              setattr(proteinEntry, 'coverageMaskShared', coverageMaskShared)