I have found many blogs to read this question , It's not clear. , What upgrade pip wait , Neither. , In fact, the solution is to uninstall first pip, Then install the installation package .
Reference resources Blog I think it's well written .
Uninstall files directly ：
sudo apt-get remove python-pip
Then go to the official website https://pypi.python.org/pypi/pip download 20.* Just the version
Such as pip-20.3.3.tar.gz Format
Unzip in the downloaded folder ：
sudo tar -zxvf pip-xxxxxx.tar.gz # Change to the name of the file you downloaded
next , In the folder you extracted , Right click to open the terminal directly , Input ：
//python2 install pip
$ sudo python setup.py install
