python爬虫需要调用什么模块

urllib.request.open(url[,data,[timeout,[cafile,[capth[,cadefault,[context]]]]]])

#coding:utf-8
import urllib.request
import time
import platform


#清屏函数(无关紧要 可以不写)
def clear():
    print(u"内容过多 3秒后清屏")
    time.sleep(3)
    OS = platform.system()
    if (OS == u'Windows'):
        os.system('cls')
    else:
        os.system('clear')
#访问函数
def linkbaidu():
    url = 'http://www.baidu.com'
    try:
        response = urllib.request.urlopen(url,timeout=3)
    except urllib.URLError:
        print(u'网络地址错误')
        exit()
    with open('/home/ifeng/PycharmProjects/pachong/study/baidu.txt','w') as fp:
        response = urllib.request.urlopen(url,timeout=3)
        fp.write(response.read())
    print(u'获取url信息，response.geturl()\n:%s'%response.getrul())
    print(u'获取返回代码，response.getcode()\n:%s' % response.getcode())
    print(u'获取返回信息，response.info()\n:%s' % response.info())
    print(u"获取的网页信息经存与baidu.txt")


if __name__ =='main':
    linkbaidu()