In Python 3, there comes a virtual environment shipped with the standard lib called venv.

to create a new venv, you can simply call:

python3 -m venv <venv-name>
virtualenv VENV_NAME  # for python 2
    --system-site-pakcages to bring system packages

to activate the venv, you need source the generated shell script

source <venv-name>/bin/activate

Note: the generated activate script contains directory infomation based on your local computer and projects, so it's NOT portable.

to deactivate it:

deactivate

But, in most times, we don't really care about the name of the virtual env, so let's simply call it .venv, and you can add the following to your .bashrc for convinence

DEFAULT_VENV_NAME=".venv"
alias create-venv="python3 -m venv $DEFAULT_VENV_NAME"
alias activate="source $DEFAULT_VENV_NAME/bin/activate"

after you activated you venv, there would be a prompt before your shell prompt. You can see that python3 and pip3 is set to the venv copy of python3 by running:

which python3 # -> .venv/bin/python3

if you run pip install, the packages will be install in your local venv directory, so no sudo needed!

since the venv directory is not portable, the best practice would be save your dependencies is your requirements.txt file.

升级 venv 中的 Python 版本

首先，你需要跳出来 venv, 到一个全局环境中，然后执行：

python3 -m venv --upgrade YOUR_VENV_DIRECTORY

这样就可以升级到对应的 Python 版本啦

移动虚拟环境

venv 把路径直接写到了 bin 中，如果重命名了文件夹，那么需要手工替换一下，以使用 sd 为例：

sd "OLD_DIR" "NEW_DIR" .venv/bin/*

Use system packages

Change in .venv/pyvenv.cfg file:

- include-system-site-packages = true
+ include-system-site-packages = true

参考

1. https://stackoverflow.com/questions/2170252/can-existing-virtualenv-be-upgraded-gracefully