docs: def extract_canonical(bs4):
      """Extracting canonical url
  
      :param bs4:
      :return:
      """
  
      link_rel = bs4.select('link[rel="canonical"]')
  
      if link_rel.__len__() > 0:
  
          if link_rel[0].has_attr('href'):
  
              return link_rel[0]['href']
  
      return None