ubuntuでpythonを最新化

ツールの準備
$ sudo apt update
$ sudo apt install build-essential libbz2-dev libdb-dev \
libreadline-dev libffi-dev libgdbm-dev liblzma-dev \
libncursesw5-dev libsqlite3-dev libssl-dev \
zlib1g-dev uuid-dev tk-dev

Python Japanのダウンロードページ
https://pythonlinks.python.jp/ja/index.html

$ tar xJf Python-3.9.６.tar.xz

$ cd Python-3.9.６
$ ./configure
$ make
$ sudo make install

確認
$ python3 -V
Python 3.9.６
$ which python3
/usr/local/bin/python3