Unable to install Python 3

[snippsat]

There also pyenv which in my option is the best way.
Have tutorial here.
When pyenv is setup,it's easy to use.

# Install
mint@mint ~ $ pyenv install 3.6.5
Downloading Python-3.6.5.tar.xz...
-> https://www.python.org/ftp/python/3.6.5/Python-3.6.5.tar.xz
Installing Python-3.6.5...
Installed Python-3.6.5 to /home/mint/.pyenv/versions/3.6.5
  
# Set python and pip to point to 3.6.5
mint@mint ~ $ pyenv global 3.6.5
mint@mint ~ $ python -V
Python 3.6.5
mint@mint ~ $ pip -V
pip 9.0.1 from /home/mint/.pyenv/versions/3.6.5/lib/python3.6/site-packages (python 3.6)
# Finish

So now will python my_script.py and pip install something always use Python 3.6.5
There is never need for sudo pip install something or pip install --user something as pyenv has set user privileges.