These days when I do crawler with Python, I always encounter Python URLError: < urlopen error timed out> The more threads open, the more frequently they occur. Later proved that the program did not have a problem, checked the information on the Internet, the network is blocked, more than a few times to try it.  
For example, the original code looks like this:

if headers:
		req=urllib2.Request(url,headers=headers)
	else :
		req=urllib2.Request(url)
	opener=urllib2.build_opener(cookieproc)
	urllib2.install_opener(opener)
	page=urllib2.urlopen(req,timeout=5).read()

can be changed after adding a loop:

if headers:
		req=urllib2.Request(url,headers=headers)
	else :
		req=urllib2.Request(url)
	opener=urllib2.build_opener(cookieproc)
	urllib2.install_opener(opener)
	global Max_Num
	Max_Num=6
	for i in range(Max_Num):
		try:
			page=urllib2.urlopen(req,timeout=5).read()
			break
		except:
			if i < Max_Num-1:
				continue
			else :
				print 'URLError: <urlopen error timed out> All times is failed '

This exception can generally be resolved