pip3升级后，运行pip 提示(warning, RequestsDependencyWarning)

问题

pip3升级后，执行 pip 会出现如下提示：

/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/__init__.py:83: RequestsDependencyWarning: Old version of cryptography ([1, 2, 3]) may cause slowdown.
warnings.warn(warning, RequestsDependencyWarning)
pip 19.1.1 from /home/rogn/.local/lib/python2.7/site-packages/pip (python 2.7)

解法

1. 升级 cryptography
sudo pip install --upgrade cryptography
2. 重新绑定pyOpenSSL（否则会出现：AttributeError: 'module' object has no attribute 'SSL_ST_INIT'）
sudo python3 -m easy_install --upgrade pyOpenSSL