大佬们能不能帮我看看这个错误怎么解决啊

WRHao

import urllib.request as urllib2

def download(url,user_agent='wswp',num_retries=2):
    print('Downloading:',url)
    headers={'User-agent:',user_agent}
    request = urllib2.Request(url,headers=headers)
    try:
        html = urllib2.urlopen (url).read()
    except urllib2.URLError as e:
        print('Downloading error:',e.reason)
        html=None
        if num_retries > 0:
            if hasattr(e,'code') and 500 <= e.code <600:
                #retry 5XX HTTP errors
                return download(url,user_agent,num_retries-1)
    return html


Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    download("https://www.cnblogs.com/")
  File "C:\Users\Desktop\爬虫初试.py", line 6, in download
    request = urllib2.Request(url,headers=headers)
  File "C:\Users\AppData\Local\Programs\Python\Python37\lib\urllib\request.py", line 334, in __init__
    for key, value in headers.items():
AttributeError: 'set' object has no attribute 'items

Stubborn

headers={'User-agent:',user_agent}   这个是个什么玩意？  写错了