code: def add_missing(self, distribution, requirement):
          
          logger.debug('%s missing %r', distribution, requirement)
          self.missing.setdefault(distribution, []).append(requirement)
docs: Add a missing *requirement* for the given *distribution*.
  
          :type distribution: :class:`distutils2.database.InstalledDistribution`
                              or :class:`distutils2.database.EggInfoDistribution`
          :type requirement: ``str``