我刚开始使用 urllib3，我马上就遇到了问题。根据他们的手册，我从一个简单的例子开始：
Python 2.7.1+ (r271:86832, Apr 11 2011, 18:13:53)
[GCC 4.5.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import urllib3
>>>
>>> http = urllib3.PoolManager()
>>> r = http.request('GET', 'http://google.com/')
我收到以下错误：
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python2.7/dist-packages/urllib3/request.py", line 65, in request
**urlopen_kw)
File "/usr/local/lib/python2.7/dist-packages/urllib3/request.py", line 78, in request_encode_url
return self.urlopen(method, url, **urlopen_kw)
File "/usr/local/lib/python2.7/dist-packages/urllib3/poolmanager.py", line 113, in urlopen
return self.urlopen(method, e.new_url, **kw)
File "/usr/local/lib/python2.7/dist-packages/urllib3/poolmanager.py", line 113, in urlopen
return self.urlopen(method, e.new_url, **kw)
File "/usr/local/lib/python2.7/dist-packages/urllib3/poolmanager.py", line 113, in urlopen
return self.urlopen(method, e.new_url, **kw)
File "/usr/local/lib/python2.7/dist-packages/urllib3/poolmanager.py", line 113, in urlopen
return self.urlopen(method, e.new_url, **kw)
File "/usr/local/lib/python2.7/dist-packages/urllib3/poolmanager.py", line 109, in urlopen
return conn.urlopen(method, url, **kw)
File "/usr/local/lib/python2.7/dist-packages/urllib3/connectionpool.py", line 309, in urlopen
raise MaxRetryError(url)
urllib3.exceptions.MaxRetryError: Max retries exceeded for url: http://google.com/
关于为什么会发生这种情况的任何线索？非常感谢。