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