\标识中的ufeff无效字符

Question

我有以下代码：

import urllib.request

try:
    url = "https://www.google.com/search?q=test"

    headers = {}
    usag = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:25.0) Gecko/20100101 Firefox/25.0'
    headers['User-Agent'] = usag.encode('utf-8-sig')
    req = urllib.request.Request(url, headers=headers)
    resp = urllib.request.urlopen(req)
    respData = resp.read()

    saveFile = open('withHeaders.txt','w')
    saveFile.write(str(respData))
    saveFile.close()

except Exception as e:
    print(str(e))

它给了我以下错误：

D:\virtualenv\samples\urllibb>python 1.py
  File "1.py", line 35
    usag = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:25.0) Gecko/20100101 Firefox/25.0'\ufeff
                                                                                              ^
 SyntaxError: invalid character in identifier

不过，我在代码中看不到\ufeff。