使用mechanize检索robots.txt时出现HTTP 403错误。

这个shell命令成功地打印出了robots.txt文件：

$ curl -A "Mozilla/5.0 (X11; Linux x86_64; rv:18.0) Gecko/20100101 Firefox/18.0 (compatible;)" http://fifa-infinity.com/robots.txt

忽略了user-agent选项会导致服务器返回403错误。检查robots.txt文件发现允许爬取http://www.fifa-infinity.com/board下的内容。然而，以下Python代码失败了：

import logging
import mechanize
from mechanize import Browser
ua = 'Mozilla/5.0 (X11; Linux x86_64; rv:18.0) Gecko/20100101 Firefox/18.0 (compatible;)'
br = Browser()
br.addheaders = [('User-Agent', ua)]
br.set_debug_http(True)
br.set_debug_responses(True)
logging.getLogger('mechanize').setLevel(logging.DEBUG)
br.open('http://www.fifa-infinity.com/robots.txt')

在我的控制台上输出如下：

No handlers could be found for logger "mechanize.cookies"
send: 'GET /robots.txt HTTP/1.1\r\nAccept-Encoding: identity\r\nHost: www.fifa-infinity.com\r\nConnection: close\r\nUser-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:18.0) Gecko/20100101 Firefox/18.0 (compatible;)\r\n\r\n'
reply: 'HTTP/1.1 403 Bad Behavior\r\n'
header: Date: Wed, 13 Feb 2013 15:37:16 GMT
header: Server: Apache
header: X-Powered-By: PHP/5.2.17
header: Vary: User-Agent,Accept-Encoding
header: Connection: close
header: Transfer-Encoding: chunked
header: Content-Type: text/html
Traceback (most recent call last):
  File "", line 1, in 
  File "/home/moshev/Projects/forumscrawler/lib/python2.7/site-packages/mechanize/_mechanize.py", line 203, in open
    return self._mech_open(url, data, timeout=timeout)
  File "/home/moshev/Projects/forumscrawler/lib/python2.7/site-packages/mechanize/_mechanize.py", line 255, in _mech_open
    raise response
mechanize._response.httperror_seek_wrapper: HTTP Error 403: Bad Behavior

奇怪的是，使用curl而不设置user-agent会导致返回"403: Forbidden"而不是"403: Bad Behavior"。

我是否做错了什么，还是mechanize/urllib2中存在bug？我不明白为什么仅仅获取robots.txt会被视为"bad behaviour"。