Create Python Virtual Environment by Python `venv`

Jul. 09, 2024

Introduction

Python venv is a lightweight virtual environment manager¹, and it is convenient to use it in some simple scenarios:

The venv module supports creating lightweight “virtual environments”, each with their own independent set of Python packages installed in their site directories. A virtual environment is created on top of an existing Python installation, known as the virtual environment’s “base” Python, and may optionally be isolated from the packages in the base environment, so only those explicitly installed in the virtual environment are available.

I’ll record some basic use of venv module in this post.

Create a virtual environment

Previously I ever installed a Spyder IDE in folder G:\Spyder, and a Python at G:\Spyder\Python311, and in which there is a python.exe. In G:\Spyder\Python311, we can open CMD and create a virtual environment, for example, called my_env, using Python venv:

python -m venv my_env

Or instead, we could specify a absolute path, like creating a virtual environment my_env into Test1 folder in desktop for example:

python -m venv C:\Users\$USER_NAME\Desktop\Test1\mv_venv

After it, a new folder called my_env is created in G:\Spyder\Python311. And in G:\Spyder\Python311\my_env, there are three sub-folders:

Include: this is a empty folder.
Lib: there is only a folder called site-packages in it, and every Python package will be installed in site-packages.
Scripts: there are 9 files in this folder, i.e. activate, activate.bat, Activate.ps1, deactivate.bat, pip.exe, pip3.11.exe, pip3.exe, python.exe, pythonw.exe. As will be showed later, operations associated with the virtual environment rely on these files.

and one file:

pyvenv.cfg

Activate the virtual environment

Then, we can activate above virtual environment my_env by command²:

my_env\Scripts\Activate.ps1

and at this time, we have got into the virtual environment:

Some references³ say that to activate the virtual environment, we should use the command:

source my_env/Srcipts/activate

however, an error occurred when I use it:

source : 无法将“source”项识别为 cmdlet、函数、脚本文件或可运行程序
的名称。请检查名称的拼写，如果包括路径，请确保路径正确，然后再试一次
。
所在位置 行:1 字符: 1
+ source my_env/Srcipts/activate
+ ~~~~~~
    + CategoryInfo          : ObjectNotFound: (source:String) [], C
   ommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

This is because command source is only available on Linux or Mac systems. For Windows systems, the above command functions².

By the way, if I just delete the source of command source my_env/Srcipts/activate, there is also a similar error:

my_env/Srcipts/activate

my_env/Srcipts/activate : 无法将“my_env/Srcipts/activate”项识别为 cmdl
et、函数、脚本文件或可运行程序的名称。请检查名称的拼写，如果包括路径，请
确保路径正确，然后再试一次。
所在位置 行:1 字符: 1
+ my_env/Srcipts/activate
+ ~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (my_env/Srcipts/activate:
   String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

So, note that on Windows systems, delimiters in file path should be \.

After activating the virtual environment, if use pip list to list the installed packages at this moment, we have:

pip list

Package    Version
---------- -------
pip        24.0
setuptools 65.5.0

The IDE software I use is Spyder; in order to use the Python interpreter of this virtual environment in Spyder, spyder-kernels package should be installed in advance⁴:

pip install spyder-kernels

here we have:

pip list

Package           Version
----------------- -----------
asttokens         2.4.1
cloudpickle       3.0.0
colorama          0.4.6
comm              0.2.2
debugpy           1.8.2
decorator         5.1.1
executing         2.0.1
ipykernel         6.29.5
ipython           8.26.0
jedi              0.19.1
jupyter_client    8.6.2
jupyter_core      5.7.2
matplotlib-inline 0.1.7
nest-asyncio      1.6.0
packaging         24.1
parso             0.8.4
pip               24.0
platformdirs      4.2.2
prompt_toolkit    3.0.47
psutil            6.0.0
pure-eval         0.2.2
Pygments          2.18.0
python-dateutil   2.9.0.post0
pywin32           306
pyzmq             26.0.3
setuptools        65.5.0
six               1.16.0
spyder-kernels    2.5.2
stack-data        0.6.3
tornado           6.4.1
traitlets         5.14.3
typing_extensions 4.12.2
wcwidth           0.2.13

Next, we can follow the steps introduced in blog⁴ to change the Python interpreter in Spyder.

Deactivate the virtual environment

At last, we can deactivate the virtual environment by:

deactivate

References