（已解决）更新pip后的报错UserWarning: Setuptools will stop working on Python 2

系统：Ubuntu

自从按照 terminal 里给的的提示 update 了 pip 后，每次使用 pip 安装东西总是报这个错：

UserWarning: Setuptools will stop working on Python 2
************************************************************
You are running Setuptools on Python 2, which is no longer
supported and
>>> SETUPTOOLS WILL STOP WORKING <<<
in a subsequent release (no sooner than 2020-04-20).
Please ensure you are installing
Setuptools using pip 9.x or later or pin to setuptools<45
in your environment.
If you have done those things and are still encountering
this message, please follow up at
https://bit.ly/setuptools-py2-warning.
************************************************************

解决办法：

参考这个github其中一网友的回复，卸载重装 pip、setuptools、wheel，使它们回到与系统 python 相适应的版本，之后不再报错。

python 3 在终端输入：

python3 -m pip uninstall pip setuptools wheel
sudo apt-get --reinstall install  python3-setuptools python3-wheel python3-pip

python 2 在终端输入：

python -m pip uninstall pip setuptools wheel
sudo apt-get --reinstall install python-setuptools python-wheel python-pip