报错1
xpath语句：
contents = response.xpath("(//div[@id='article_content']/text()) | (//div[@id='article_content']/br) ｜ (//div[@id='article_content']/p/img)").extract()
报错：
ValueError: All strings must be XML compatible: Unicode or ASCII, no NULL bytes or control characters
解决办法：
contents = response.xpath(u"(//div[@id='article_content']/text()) | (//div[@id='article_content']/br)|(//div[@id='article_content']/p/img)").extract()
