pip安装包时，报错ModuleNotFoundError: No module named ‘_ctypes‘的解决办法

原因：缺少 libffi-devel

执行如下命令：

yum install libffi-devel 

./configure prefix=/usr/local/python3

make && make install

ln -s /usr/local/python3/bin/python3.9 /usr/bin/python3

ln -s /usr/local/python3/bin/pip3.9 /usr/bin/pip3