はじめに

Ubuntu 20.04にPython 3.8をインストール

LOG

インストール

# cat /etc/os-release
NAME="Ubuntu"
VERSION="20.04 LTS (Focal Fossa)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 20.04 LTS"
VERSION_ID="20.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=focal
UBUNTU_CODENAME=focal

# apt update; apt install -y python3
... 略

各種確認

# which python{,2,3}
/usr/bin/python3

# ll /usr/bin/python*
lrwxrwxrwx. 1 root root       9 Mar 13 12:20 /usr/bin/python3 -> python3.8*
-rwxr-xr-x. 1 root root 5457568 Mar 13 10:14 /usr/bin/python3.8*

# python3 -V
Python 3.8.2

# apt show python3
Package: python3
Version: 3.8.2-0ubuntu2
Priority: important
Section: python
Source: python3-defaults
Origin: Ubuntu
Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
Original-Maintainer: Matthias Klose <doko@debian.org>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 194 kB
Provides: python3-profiler
Pre-Depends: python3-minimal (= 3.8.2-0ubuntu2)
Depends: python3.8 (>= 3.8.2-1~), libpython3-stdlib (= 3.8.2-0ubuntu2)
Suggests: python3-doc (>= 3.8.2-0ubuntu2), python3-tk (>= 3.8.2-1~), python3-venv (>= 3.8.2-0ubuntu2)
Replaces: python3-minimal (<< 3.1.2-2)
Homepage: https://www.python.org/
Task: minimal, ubuntu-core
Download-Size: 47.6 kB
APT-Manual-Installed: yes
APT-Sources: http://archive.ubuntu.com/ubuntu focal/main amd64 Packages
Description: interactive high-level object-oriented language (default python3 version)

補足

Ubuntu20.04にPython3.9が出てきそうなので、 apt install -y python3.8 とやるほうが確実かもしれない
ただしその場合 /usr/bin/python3 は作成されないようなので注意。