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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 resolve_filename(self, package_dir, filename):
 """Gets a proper full relative path of Sass source and CSS source that will be generated, according to ``package_dir`` and ``filename``. :param package_dir: the path of package directory :type package_dir: :class:`str`, :class:`basestring` :param filename: the filename of Sass/SCSS source to compile :type filename: :class:`str`, :class:`basestring` :returns: a pair of (sass, css) path :rtype: :class:`tuple` """

        sass_path = os.path.join(package_dir, self.sass_path, filename)
        if self.strip_extension:
            filename, _ = os.path.splitext(filename)
        css_filename = filename + '.css'
        css_path = os.path.join(package_dir, self.css_path, css_filename)
        return sass_path, css_path