我已經(jīng)寫了一個(gè)蜘蛛，但是每當(dāng)我運(yùn)行這個(gè)蜘蛛時(shí)，我都會(huì)得到這個(gè)錯(cuò)誤：Traceback (most recent call last):  File "/usr/local/lib/python2.7/dist-packages/twisted/internet/base.py", line 824, in runUntilCurrent    call.func(*call.args, **call.kw)  File "/usr/local/lib/python2.7/dist-packages/twisted/internet/task.py", line 607, in _tick    taskObj._oneWorkUnit()  File "/usr/local/lib/python2.7/dist-packages/twisted/internet/task.py", line 484, in _oneWorkUnit    result = next(self._iterator)  File "/usr/local/lib/python2.7/dist-packages/scrapy/utils/defer.py", line 57, in <genexpr>    work = (callable(elem, *args, **named) for elem in iterable)--- <exception caught here> ---  File "/usr/local/lib/python2.7/dist-packages/scrapy/utils/defer.py", line 96, in iter_errback    yield it.next()  File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spidermiddleware/offsite.py", line 28, in process_spider_output    for x in result:  File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spidermiddleware/referer.py", line 22, in <genexpr>    return (_set_referer(r) for r in result or ())  File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spidermiddleware/urllength.py", line 33, in <genexpr>    return (r for r in result or () if _filter(r))  File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spidermiddleware/depth.py", line 50, in <genexpr>    return (r for r in result or () if _filter(r))  File "/home/vaibhav/scrapyprog/comparison/eScraperInterface/eScraper/spiders/streetstylestoreSpider.py", line 38, in parse    item['productURL'] = site.select('.//a/@href').extract()exceptions.AttributeError: 'unicode' object has no attribute 'select'