def get_song_currency(self, cache=True):
        """
        Args:
            cache (bool): A boolean indicating whether or not the cached value should be used (if available). Defaults to True.
        
        Returns:
            A float representing a song's currency rank.
            
        Example:
            >>> s = song.Song('SOQKVPH12A58A7AF4D')
            >>> s.get_song_currency()
            0.639626025843539
            >>> s.song_currency
            0.639626025843539
            >>>
        """
        if not (cache and ('song_currency' in self.cache)):
            response = self.get_attribute('profile', bucket='song_currency')
            self.cache['song_currency'] = response['songs'][0]['song_currency']
        return self.cache['song_currency']