pip 升级 pip 失败

今天在使用 python pip 安装一个 python 包的时候,一直提示:

# pip install --upgrade pip
Requirement already up-to-date: pip in /usr/local/lib/python2.7/dist-packages
You are using pip version 8.1.1, however version 8.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

尝试按说明执行 pip …

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