First, check wheater you have installed python and what version it is.
Second, according to your operating system and your own need to choose which version to install and the way to install.
Sometimes, you shoulde be careful about knowing the link python python3 python2 and so on that which version they are really pointing.
sudo pacman -S python-pip
pip install pip -U pip config set global.index-url https://pypi.tuna.tsinghua.edu.cn/simple