code: def package_type(self):
          
          mapping = {'bdist_egg': u'egg', 'bdist_wheel': u'wheel',
                     'sdist': u'source'}
          ptype = self._release['packagetype']
          if ptype in mapping.keys():
              return mapping[ptype]
          return ptype
docs: >>> package = yarg.get('yarg')
              >>> v = "0.1.0"
              >>> r = package.release(v)
              >>> r.package_type
              u'wheel'