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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 rel_to_abs(self, base_url):
 """ Converts relative links from css contents to absolute links :param base_url: The base page url to use for building absolute links :type base_url: str :param css_contents: The CSS contents to parse :type css_contents: str """

        self.cleaned_css = self.rel_to_abs_re.sub(
            lambda match: "url('%s')" % urljoin(
                base_url, match.group('path').strip('\'"')),
            self.cleaned_css)