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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_allowed_domain(url, allow_subdomains=True):
 """ Determines the url's domain. :param str url: the url to extract the allowed domain from :param bool allow_subdomains: determines wether to include subdomains :return str: subdomains.domain.topleveldomain or domain.topleveldomain """

        if allow_subdomains:
            return re.sub(re_www, '', re.search(r'[^/]+\.[^/]+', url).group(0))
        else:
            return re.search(re_domain, UrlExtractor.get_allowed_domain(url)).group(0)