解决python2.x用urllib2证书验证错误, _create_unverified_context

错误1：AttributeError: 'module' object has no attribute '_create_unverified_context'，

错误2：URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:661)>

import ssl

try:
    _create_unverified_https_context = ssl._create_unverified_context
except AttributeError:
    # Legacy Python that doesn't verify HTTPS certificates by default
    pass
else:
    # Handle target environment that doesn't support HTTPS verification
    ssl._create_default_https_context = _create_unverified_https_context

官方解释：

This guidance is aimed primarily at system administrators that wish to adopt newer 
versions of Python that implement this PEP in legacy environments that do not yet 
support certificate verification on HTTPS connections. For example, an administrator 
may opt out by adding the monkeypatch above to sitecustomize.py in their Standard 
Operating Environment for Python. Applications and libraries SHOULD NOT be making 
this change process wide (except perhaps in response to a system administrator 
controlled configuration setting).

Particularly security sensitive applications should always provide an explicit 
application defined SSL context rather than relying on the default behaviour 
of the underlying Python implementation.