too many values to unpack 错误

python 3.6，用urllib库尝试爬取url

url="http://blog.csdn.net/weiwei_pig/article/details/51178226"

headers=("User-Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/
537.36")
opener=urllib.request.build_opener()

opener.addheaders=[headers]
data=opener.open(url).read()

错误提示如下：
Traceback (most recent call last):
File "/Users/nathanlu/PycharmProjects/learn/spider.py", line 27, in
data=opener.open(url).read()
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/urllib/request.py", line 524, in open
req = meth(req)
File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/urllib/request.py", line 1269, in do_request_
for name, value in self.parent.addheaders:
ValueError: too many values to unpack (expected 2)

请问什么原因？

https://stackoverflow.com/questions/7053551/python-valueerror-too-many-values-to-unpack

headers=("User-Agent","Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/
537.36")