问为什么总是显示：can't concat str to bytes 请问是哪里出错了呢？

import urllib.request

import os

def url_open(url):

head={}

head['User-Agent']=' Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.116 Safari/537.36'

req=urllib.request.Request(url,head)

response=urllib.request.urlopen(req)

html=response.read()

return html

#找图片对应的规律

def get_page(url):

html=url_open(url).decode('utf-8')

a=html.find('current')+9

b=html.find('<',a)

return html[a:b]

#寻找图片地址

def find_imgs(url):

html=url_open(url).decode('utf-8')

img_addrs=[]

a=html.find('img src=')

while a!=-1:

b=html.find('.jpg',a,a+255)

if b!=-1:

img_addrs.append(html[a+9:b+4])

else:

b=a+9

a=html.find('img src=',b)

return img_addrs

#保存图片

def save_imgs(folder,img_adders):

for each in img_addrs:

filename=each.split('/')[-1]

with open(filename,'wb') as f:

img=url_open(each)

f.write(img)

def download(folder='照片合集',pages=30):

os.mkdir(folder)

os.chdir(folder)

url='https://www.7160.com/xingganmeinv/'

page_num=int(get_page(url))

for i in range(pages):

page_num+=i

page_url=url+'list_3_'+str(page_num)+'.html'

#img是将图片地址保存为列表

img_addrs=find_imgs(page_url)

save_imgs(folders,img_addrs)

#测试函数

if __name__=='__main__':

download()