爬虫：代码没有报错，但是文件夹下没有图片

我才是小宝啊

代码如下：
import urllib.request
import os

def url_open(url):
    req = urllib.request.Request(url)
    req.add_header('User-Agent','Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.102 Safari/537.36 Edge/18.19041')
    respone = urllib.request.urlopen(req)
    html = respone.read()
    return html

def find_img(url):
    html = url_open(url).decode('utf-8')
    img_addrs = []
    a = html.find('src=')
    while a != -1:
        b = html.find('.jpg',a,a+255)
        if b != -1:
            html2 = 'http:'+html[a+5:b+4]
            img_addrs.append(html2)
        else:
            b = a+5  
        a = html.find('src=',b)
        return(img_addrs)


def save_img(folder,img_addrs):
    for each in img_addrs:
        filename = each.split('/')[-1]
        with open(filename,'wb') as f:      
            img = url_open(each)
            f.write(img)


def download_ww(folder = 'pic'):
    os.mkdir(folder)
    os.chdir(folder)
   
    url = 'http://jandan.net/pic/'
   
    for i in range(3):
        page_url = url +'MjAyMDEyMTUtMTk'+str(i)+'#comments'
        img_addrs = find_img(page_url)
        save_img(folder,img_addrs)

if __name__ == '__main__':
    download_ww()


代码没有报错，但是文件夹下没有图片，请问是什么问题

suchocolate

# _*_ coding: utf-8 _*_

import urllib.request
import re
import os


def ck_dir(folder='pic'):
    if not os.path.exists(folder):
        os.mkdir(folder)
    os.chdir(folder)


def main():
    ck_dir()
    url = 'http://jandan.net/pic'
    for i in range(3):
        req = urllib.request.Request(url)
        req.add_header('user-agent', 'mozilla')
        r = urllib.request.urlopen(req)
        html = r.read().decode('utf-8')
        result = re.findall(r'<img src="(.*?)"', html)
        nx_page = re.findall(r'href="(.*?)" class="previous', html)[0]
        url = 'http:' + nx_page
        dl_img(result)


def dl_img(ls):
    for item in ls:
        img_url = 'http:' + item
        img_name = item.split('/')[-1]
        urllib.request.urlretrieve(img_url, img_name)


if __name__ == '__main__':
    main()