1. The system comes with python2.7 and python3.5, and the default for running python directly is version 2.7
Of course, the default version of running python directly can be modified, refer to here
Then you may need version 3.6, just enter it directly on the command line
sudo apt install python3.6
Downloaded here is 3.6.2
Similarly, change the version number to 2.7 and 3.5 to download the 2.7 and 3.5 versions of python
Use the following command
python3.6 XX.py
Uninstall with the following command
sudo apt remove python3.6
Of course, the 2.7 and 3.5 versions are uninstalled carefully, because there may be dependencies at the bottom of the system
2. pip is a tool used to easily download some python packages
However, different versions of python have different pips.
The pip installation command for python2.7: sudo apt install python-pip
The pip installation command for python3.5: sudo apt install python3-pip
The python3.6 installation comes with pip
The pip installation toolkit for a specific version (3.6 for example):
python3.6 -m pip install SomePackage
Specific reference here