def make_series_url(key):
    """For internal use. Given a series key, generate a valid URL to the series
    endpoint for that key.

    :param string key: the series key
    :rtype: string"""

    url = urlparse.urljoin(endpoint.SERIES_ENDPOINT, 'key/')
    url = urlparse.urljoin(url, urllib.quote(key))
    return url