python3 使用urllib报错urlopen error EOF occurred in violation of protocol (_ssl.c:841)

python3源码：

import urllib.request
from bs4 import BeautifulSoup

response = urllib.request.urlopen("http://php.net/")
html = response.read()
soup=BeautifulSoup(html, "html5lib")
text=soup.get_text(strip=True)
print(text)

　　代码很简单，就是抓取http://php.net/页面文本内容，然后使用BeautifulSoup模块清除过滤掉多余的html标签。貌似第一次允许成功了，之后一直卡着再报错：

  File "C:\Python36\lib\urllib\request.py", line 504, in _call_chain
    result = func(*args)
  File "C:\Python36\lib\urllib\request.py", line 1361, in https_open
    context=self._context, check_hostname=self._check_hostname)
  File "C:\Python36\lib\urllib\request.py", line 1320, in do_open
    raise URLError(err)
urllib.error.URLError: <urlopen error EOF occurred in violation of protocol (_ssl.c:841)>

　　实际上google浏览器是能够访问的。

　　此问题可能是由于Web服务器上禁用了SSLv2，而比较老的python库Python 2.x尝试默认情况下与PROTOCOL_SSLv23建立连接。因此在这种情况下，需要选择请求使用的SSL版本。

　　要更改HTTPS中使用的SSL版本，需要将该HTTPAdapter类子类化并将其挂载到 Session对象。例如，如果想强制使用TLSv1，则新的传输适配器将如下所示：

from requests.adapters import HTTPAdapter
from requests.packages.urllib3.poolmanager import PoolManager

class MyAdapter(HTTPAdapter):
    def init_poolmanager(self, connections, maxsize, block=False):
        self.poolmanager = PoolManager(num_pools=connections,
                                       maxsize=maxsize,
                                       block=block,
                                       ssl_version=ssl.PROTOCOL_TLSv1)

　　然后，可以将其挂载到Requests Session对象：

s=requests.Session()
s.mount('https://', MyAdapter())
response = urllib.request.urlopen("http://php.net/")

　　编写一个通用传输适配器还是很简单，它可以从ssl构造函数中的包中获取任意SSL类型并使用它。

from requests.adapters import HTTPAdapter
from requests.packages.urllib3.poolmanager import PoolManager

class SSLAdapter(HTTPAdapter):
    '''An HTTPS Transport Adapter that uses an arbitrary SSL version.'''
    def __init__(self, ssl_version=None, **kwargs):
        self.ssl_version = ssl_version

        super(SSLAdapter, self).__init__(**kwargs)

    def init_poolmanager(self, connections, maxsize, block=False):
        self.poolmanager = PoolManager(num_pools=connections,
                                       maxsize=maxsize,
                                       block=block,
                                       ssl_version=self.ssl_version)

　　修改后的上述出错的代码：

import urllib.request
from bs4 import BeautifulSoup
import requests
from requests.adapters import HTTPAdapter
from requests.packages.urllib3.poolmanager import PoolManager
import ssl

class MyAdapter(HTTPAdapter):
    def init_poolmanager(self, connections, maxsize, block=False):
        self.poolmanager = PoolManager(num_pools=connections,
                                       maxsize=maxsize,
                                       block=block,
                                       ssl_version=ssl.PROTOCOL_TLSv1)

s=requests.Session()
s.mount('https://', MyAdapter())
response = urllib.request.urlopen("http://php.net/")
html = response.read()
soup=BeautifulSoup(html, "html5lib")
text=soup.get_text(strip=True)
print(text)

　　可以正常抓取网页文本信息。