def find_first_version(self):
for version in self.versions_to_try:<EOL><INDENT>remote_url = self.get_download_url(version=version)<EOL>if http_url_exists(remote_url):<EOL><INDENT>return version, remote_url<EOL><DEDENT><DEDENT>return None, None<EOL>
Finds the first version of igraph that exists in the nightly build
        repo from the version numbers provided in ``self.versions_to_try``.