Defaulting to user installation because normal site-packages is not writeable
原因：
没有操作 site-packages 目录权限
解决方法：
命令前加上 sudo
sudo pip3 install CommandNotFound
- site-packages installation Defaulting writeable packagessite-packages installation defaulting writeable site-packages future site-packages annotations packages packages fastjsonschema site-packages anaconda3 crypto_num_locks site-packages undefined packages 39 bson get_object_size site-packages apscheduler python3 python site-packages markupsafe 39 site-packages soft_unicode site-packages packages位置 目录 directory packages install oserror