爬虫系列15、为链接添加一个回调函数类

class ScrapeCallback:
def __init__(self):
self.writer = csv.writer(open('countries.csv','w'))
# 表头
self.fields = ('area', 'ranked', 'university')
self.writer.writerow(self.fields)
def __call__(self, url, html):
if re.search('/view/',url):
tree = lxml.html.fromstring(html)
row = []
for field in self.fields:
row.append(tree.cssselect('table > tr#places_{}_row > td.w2p_fw'.format(field))
[0].text_content())
self.writer.writerow(row)