在cmd窗口输入 pip install beautifulsoup4,如下：
C:\Users\horn1\Desktop\python\3>pip install beautifulsoup4
Collecting beautifulsoup4
Downloading beautifulsoup4-4.6.0-py3-none-any.whl (86kB)
100% |████████████████████████████████| 92kB 225kB/s
Installing collected packages: beautifulsoup4
Successfully installed beautifulsoup4-4.6.0
You are using pip version 9.0.1, however version 9.0.3 is available.
You should consider upgrading via the 'python -m pip install --upgrade pip' command.