Python pip 报错

1，pip ssl certification ssl: certificate_verify_failed。。。

2，Could not find a version that satisfies the requirement Flask-B

ootstrap==3.0.3.1 (from -r common.txt (line 2)) (from versions: )

No matching distribution found for Flask-Bootstrap==3.0.3.1 (from
-r common.txt (line 2))

解决：

pip --trusted-host pypi.python.org install virtualenv