code: def requires(self, extras=()):
          
          dm = self._dep_map
          deps = []
          deps.extend(dm.get(None, ()))
          for ext in extras:
              try:
                  deps.extend(dm[safe_extra(ext)])
              except KeyError:
                  raise UnknownExtra(
                      "%s has no such extra feature %r" % (self, ext)
                  )
          return deps
docs: List of Requirements needed for this distro if `extras` are used