code: def build(self, update=True):
          
          ret = self.base + self.query
          page = "".join(("/", str(self.page), "/"))
  
          if self.category:
              category = " category:" + self.category
          else:
              category = ""
  
          if self.order:
              order = "".join(("?field=", self.order[0], "&sorder=", self.order[1]))
          else:
              order = ""
  
          ret = "".join((self.base, self.query, category, page, order))
  
          if update:
              self.max_page = self._get_max_page(ret)
          return ret
docs: Build and return url. Also update max_page.