Why can't I install Python 3.8? [duplicate]

When I try to install Python 3.8 terminal says it is done, but when I run python --version it says Python 3.7.

(base) user@admin:~$ sudo apt-get install python3.8
Reading package lists... Done
Building dependency tree
Reading state information... Done
python3.8 is already the newest version (3.8.2-1ubuntu1.2).
The following packages were automatically installed and are no longer required: libllvm9 libllvm9:i386
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 38 not upgraded.

(base) user@admin:~$ python --version
Python 3.7.6

2 Answers

As per the instructions on How to Install Python 3.8 on Ubuntu, Debian and LinuxMint – TecAdmin, try the following:

Prerequisites:

Install [and or update] the following packages; build-essential, checkinstall, libreadline-gplv2-dev, libncursesw5-dev, libssl-dev, libsqlite3-dev, tk-dev, libgdbm-dev, libc6-dev, libbz2-dev, libffi-dev, zlib1g-dev.

sudo apt install build-essential checkinstall
sudo apt-get install libreadline-gplv2-dev libncursesw5-dev libssl-dev libsqlite3-dev tk-dev libgdbm-dev libc6-dev libbz2-dev libffi-dev zlib1g-dev

Thereafter, change directory (cd) to your opt folder [or any convenient folder] and download the python source code from python's server:

First change directory (cd) to the 'opt' folder:

cd /opt/

Download the source code

sudo wget 

Extract the [downloaded] source code files

sudo tar xzf Python-3.8.3.tgz

Change directory (cd) the Python Folder [created after the extraction]

cd Python-3.8.3

Compile the source code

sudo ./configure --enable-optimizations

then

sudo make altinstall

Once the compilation is completed, you can confirm that Python 3.8 has been installed successfully with:

python3.8 -V

You should see the response Python-3.8.3.

However, to precisely answer your question, python 3.8 isn't available via ubuntu official repos. You would have to add a PPA to get python 3.8 using sudo apt install [python3.x.x].

The process is described on How to Install Python 3.8 on Ubuntu 18.04 | Linuxize

Hope this helps and I hope I answered your question adequately.

It looks like Python 3.8 is already installed but not set as default. Python 3.7.6 is set as default.

Update default Python3 version by below command.

sudo update-alternatives --config python3

Choose Python 3.8 option and check Python version again.