UbuntuにPython3.8とvenvの仮想環境をインストールする

$ sudo apt-get update
$ sudo apt-get install python3.8

# こうすると3.6.9がインストールできる
$ sudo apt-get remove python3

$ python3.8 --version
Python 3.8.0

$ sudo apt-get update
$ sudo apt-get install python3.8

$ python3.8 --version
Python 3.8.0

$ sudo apt install python3.8-venv

# まずは仮想環境の名前を決める。
$ python3.8 -m venv my-project-env

# ディレクトリを移動して
$ cd path/to/my-project

# そこを仮想環境とする
$ source my-project-env/bin/activate
(my-project-env) suzu6:~/path/to/my-project$ 

(my-project-env) suzu6:~/path/to/my-project$  python --version
Python 3.8.0

(my-project-env) suzu6:~/path/to/my-project$ pip -V
pip 9.0.1 from /home/suzumura/git/nuxt-blog/my-project-env/lib/python3.8/site-packages (python 3.8)

# NumPyとMatplotlibをインストール
(my-project-env) suzu6:~/path/to/my-project$ pip install numpy matplotlib

# バージョン確認
(my-project-env) suzu6:~/path/to/my-project$ pip freeze
cycler==0.10.0
kiwisolver==1.1.0
matplotlib==3.2.0
numpy==1.18.2
pkg-resources==0.0.0
pyparsing==2.4.6
python-dateutil==2.8.1
six==1.14.0

# 仮想環境を閉じる
(my-project-env) suzu6:~/path/to/my-project$ deactivate

# 仮想環境を削除する
$ rm -r my-project-env

$ python3.8 -m venv -h
usage: venv [-h] [--system-site-packages] [--symlinks | --copies] [--clear] [--upgrade] [--without-pip] [--prompt PROMPT] ENV_DIR [ENV_DIR ...]

Creates virtual Python environments in one or more target directories.

positional arguments:
  ENV_DIR               A directory to create the environment in.

optional arguments:
  -h, --help            show this help message and exit
  --system-site-packages
                        Give the virtual environment access to the system site-packages dir.
  --symlinks            Try to use symlinks rather than copies, when symlinks are not the default for the platform.
  --copies              Try to use copies rather than symlinks, even when symlinks are the default for the platform.
  --clear               Delete the contents of the environment directory if it already exists, before environment creation.
  --upgrade             Upgrade the environment directory to use this version of Python, assuming Python has been upgraded in-place.
  --without-pip         Skips installing or upgrading pip in the virtual environment (pip is bootstrapped by default)
  --prompt PROMPT       Provides an alternative prompt prefix for this environment.

Once an environment has been created, you may wish to activate it, e.g. by sourcing an activate script in its bin directory.