python 获取地图信息

# -*-coding:utf-8-*-import urllibimport urllib2import jsondef download_pois(keywords,types,city,children,offset,page,extensions,key):    keywords = keywords    types = types       city = city    children = children    offset = offset    page = page    extensions  = extensions    key = key    # keywords =  '北京大学'    # types = '高等院校'    # city = '北京'    # children = 1    # offset = 20    # page = 1    # extensions = 'all'    # key ='b9ca5e60b99fda0fc6fac6644f88c814'    url = 'http://restapi.amap.com/v3/place/text?key='+str(key)+'&keywords='+str(keywords)+'&types='+str(types)+'&city='+str(city)+'&children='+str(children)+'&offset='+str(offset)+'&page'+str(page)+'&extensions='+str(extensions)    response = urllib2.urlopen(url)    res = response.read()    file = open('1.txt','wb')    file.write(res)    file.close()if __name__ == '__main__':    download_pois('北京大学','高等院校','北京','1','20','1','all','b9ca5e60b99fda0fc6fac6644f88c814')

如何让输出的文件 json格式化呢？