I tried apt install python 3.9 and it replied:
Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package python3.9 E: Couldn't find any package by glob 'python3.9' E: Couldn't find any package by regex 'python3.9' If you are on Ubuntu 19.10 (Eoan Ermine) (or any other version unsupported by the deadsnakes PPA), you will not be able to install using the deadsnakes PPA.
What you can do instead, is get the source from Python's official website, and install it manually, as described here.
To do so, first, install the dependencies required to build the Python package.
sudo apt install build-essential zlib1g-dev \ libncurses5-dev libgdbm-dev libnss3-dev \ libssl-dev libreadline-dev libffi-dev curl software-properties-common Then download the tarball and extract it:
wget https://www.python.org/ftp/python/3.9.0/Python-3.9.0.tar.xz tar -xf Python-3.9.0.tar.xz Then cd to the extracted directory:
cd Python-3.9.0 Now configure the script:
./configure Now, to install Python 3.9 alongside your current Python installation (if any), use:
sudo make altinstall Lastly, you can verify your installation using
python3.9 --version How to make python3.X default of Python 3? (Optional)
rm /usr/bin/python3 ln -s /usr/bin/python3.5 /usr/bin/python3 alias python3='/usr/bin/python3.9' or
alias python3='/usr/local/bin/python3.9' 
python3 is symbolic link to some version of python, so you can 1) sudo unlink /usr/bin/python3 2) sudo ln -s /usr/bin/python3.9 /usr/bin/python3
tkinter. The solution was to brute-force uninstall python3.9, sudo apt install tk-dev tcl-dev and then reinstall python3.9 as explained above. So, I suggest for anybody to add tk-dev tcl-dev to the list of packages to be installed in the first command of this answer.sudo apt install build-essential zlib1g-dev libncurses5-dev libgdbm-dev libnss3-dev libssl-dev libreadline-dev libffi-dev curl software-properties-common tk-dev tcl-dev libsqlite3-dev
You are getting that error because you first need to update the package list and the prerequisites.
sudo apt update sudo apt install software-properties-common Then, add the repository ppa:deadsnakes/ppa to your sources list (where you will download Python from)
sudo add-apt-repository ppa:deadsnakes/ppa Make sure to press Enter when prompted. Then update available the packages:
sudo apt update Lastly, install the version of your choice:
sudo apt install python3.9 Make sure to read this:
Disclaimer: there's no guarantee of timely updates in case of security problems or other issues. If you want to use them in a security-or-otherwise-critical environment (say, on a production server), you do so at your own risk.
sudo apt update before sudo apt install python3.9, or it still will not locate the package
I have spent a long time searching for this but found the answer here first: https://github.com/baralraj/python-3.9-on-wsl/blob/main/README.md
1st: Update and install some required packages that are needed to build python from source.
sudo apt update sudo apt upgrade sudo apt install build-essential zlib1g-dev libncurses5-dev libgdbm-dev libnss3-dev libssl-dev libreadline-dev libffi-dev wget 2nd: Create a temp directory, download the python source code and unzip (I usually just download it manually from that url in the browser and unzip it with the files UI)
mkdir ~/tmp cd ~/tmp wget https://www.python.org/ftp/python/3.9.12/Python-3.9.12.tgz tar -xvzf Python-3.9.12.tgz 3rd: Configure and install
cd Python-3.9.12 ./configure sudo make altinstall 4th: check the installation
python3.9 --version Output should be
Python 3.9.12
