python爬虫用selenium访问一个网址返回的是个json字符串，怎么获取这个json字符串？

#-*- coding:utf-8 -*-
from bs4 import BeautifulSoup
from selenium import webdriver


driver=webdriver.Chrome()
driver.get('https://www.zhihu.com/api/v4/members/qing-shi-yong-zhen-shi-xing-ming/followees?offset=0&limit=20')
html = driver.page_source

soup = BeautifulSoup(html, 'lxml')
cc = soup.select('pre')[0]
print cc.string