I presume you are a Linux user. I faced a similar issue when I was trying to install Python
3.9 but when I ran python -V in the terminal, it would tell me I had version 2.
I can't guarantee
this will work but it worked for me. If you are using Ubuntu 20.04 a Linux distro, by default you have Python 3.9. In Ubuntu 18 and 16 there is also a Python version pre-installed. In your case, you need to first uninstall Python 3.
Using this command in the terminal.
sudo apt-get remove --purge python3
After uninstalling, reinstall as Python 3.9 version using this command:
sudo apt update
sudo apt install software-properties-common
sudo add-apt-repository ppa:deadsnakes/ppa
sudo apt install python3.9
python3.9 --version
Again if you're using an editor like Pycharm your base interpreter will be messed up! So please be careful when uninstalling.
And this code works on Ubuntu which I presume is what you are working on.
Another thing you need to install a repository to get Py 3.9. it's called deadsnakes I've mentioned the code above on how you could install it.
I hope you faced no issues. Remember it worked for me but I'm not sure it will work for you. Enjoy with Python 3.9 if the installation is successful :)