处理地址异常

from urllib.request import urlopen
from urllib.error import HTTPError,URLError
from bs4 import BeautifulSoup
'''
如果想用HTTPError和URLError一起捕获异常，那么需要将HTTPError放在URLError的前面，
因为HTTPError是URLError的一个子类。如果URLError放在前面，出现HTTP异常会先响应URLError，
这样HTTPError就捕获不到错误信息了
'''
def getTitle(url):
    try:
        html = urlopen(url)
    except HTTPError as e:
        print('HTTPError:%s'%e.code)
        return None
    except URLError as e:
        print('URLError:%s'%e.code)
    try:
        bsObj = BeautifulSoup(html,'html.parser')
        title = bsObj.body.h12
        import pdb
        pdb.set_trace()
    except AttributeError as e:
        print('AttributeError:%s'%e.code)
        return None
    print('1')
    return title
title = getTitle("http://www.pythonscraping.com/pages/page1.html")
if title == None:
    print("Title could not be found")
else:
    print(title)