ah_bootstrap.py 文件源码

def _do_upgrade(self, dist):
        # Build up a requirement for a higher bugfix release but a lower minor
        # release (so API compatibility is guaranteed)
        next_version = _next_version(dist.parsed_version)

        req = pkg_resources.Requirement.parse(
            '{0}>{1},<{2}'.format(DIST_NAME, dist.version, next_version))

        package_index = PackageIndex(index_url=self.index_url)

        upgrade = package_index.obtain(req)

        if upgrade is not None:
            return self._do_download(version=upgrade.version)