select方法能用css选择器，非常友好，于是想对比一下是否效率上更优秀
s1=time.time()
star=[x.text for x in bs_info.find_all('span',{'class':'rating_num'})]
e1 = time.time()
print(e1-s1)
s2 = time.time()
star = [x.text for x in bs_info.select('body span.rating_num')]
e2 = time.time()
print(e2 - s2)
exit()
可见find_all速度比select快了1倍