Python coding

Using virtual environments

last updated: 2026-07-19

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Intro

My software to create static homepages from markdown files called PYSHPCREATOR (PYthon Simple HomePage CREATOR) did not run with newer Python versions because of some older libraries.

A virtual environment helps with such problems, because it isolates the project from other environments, including the global interpreter environment. So no more complications from conflicting package versions, and the possibility to use an older python version. More in the python docs: https://docs.python.org/3/library/venv.html.

How to create a virtual environment?

Let's create a virtual environment in our software folder (e.g. pyshpcreator/Python) It is good to install the virtual environment in a separate folder (e.g. .venv)), so it can be excluded if versioning with e.g. git.

    cd ~/pyshpcreator/Python
    python -m venv .venv

In the bin directory in the .venv folder I see that python 3.12 was used and pip is there to install further packages.

Activate the virtual environment

To work in our virtual environment, we have to activate it:

    cd ~/pyshpcreator/Python
    source .venv/bin/activate

Now we remark the following prefix before our promt: (.venv).

Installing modules in the virtual environment

Now we can install our missing modules (e.g. markdown2, pygments) with pip:

    pip install markdown2 pygments

After installing all the modules we can check the requirement (all the modules) with the following command:

    python3 -m pip freeze

Here we see the output for my PYSHPCREATOR software:

    bcrypt==4.2.1
    beautifulsoup4==4.12.3
    bs4==0.0.2
    certifi==2025.1.31
    cffi==1.17.1
    charset-normalizer==3.4.1
    cryptography==44.0.0
    idna==3.10
    markdown2==2.5.2
    paramiko==3.5.0
    pycparser==2.22
    Pygments==2.19.1
    PyNaCl==1.5.0
    requests==2.32.3
    soupsieve==2.6
    urllib3==2.3.0

Or better we can create a file called requirements.txt containing all the requirements:

    pip3 freeze > requirements.txt

Using a downloaded program that contains a requirements.txt file

If a requirements.txt file is given by the maintainer of the software, it is easy to recreate the modules in a new virtual environment. When you create the virtual environment, you need to use the same python version than the maintainer, otherwise it is possible that module versions will not fit!

First download the repo from github, create and activate the virtual environment:

    cd ~
    git clone https://github.com/weigu1/pyshpcreator.git
    cd pyshpcreator/Python
    python -m venv .venv
    source .venv/bin/activate

Now we can install all the dependencies with:

    python3 -m pip install -r requirements.txt

Finally we open the program withNow we can open the program with:

    python pyshpcreator.py

Leave the virtual environment

We leave with:

    deactivate

Renewing a virtual environment and updating the modules

When I updated my computer with a new Kubuntu version, my old environment did not work anymore due to incompatible python versions. I got this error:

Could not find platform independent libraries <prefix>
Could not find platform dependent libraries <exec_prefix>
Fatal Python error: Failed to import encodings module
Python runtime state: core initialized
ModuleNotFoundError: No module named 'encodings'

So first I deleted the od .venv folder and created a new environment and entered it:

    python3 -m venv .venv
    source .venv/bin/activate

I tried to reinstall all the modules with pip:

    python3 -m pip install -r requirements.txt

This gave me an error with the cffi module. Removing the line with cffi from requirements.txt did the trick.

A check with python3 -m pip freeze showed that cffi was installed with a newer version.

So I checked the other modules with: 

    pip list --outdated

Here the result:

    Package            Version   Latest    Type
    ------------------ --------- --------- -----
    bcrypt             4.2.1     5.0.0     wheel
    beautifulsoup4     4.12.3    4.15.0    wheel
    certifi            2025.1.31 2026.6.17 wheel
    charset-normalizer 3.4.1     3.4.9     wheel
    cryptography       44.0.0    49.0.0    wheel
    idna               3.10      3.18      wheel
    markdown2          2.5.2     2.5.5     wheel
    paramiko           3.5.0     5.0.0     wheel
    pip                25.1.1    26.1.2    wheel
    pycparser          2.22      3.0       wheel
    Pygments           2.19.1    2.20.0    wheel
    PyNaCl             1.5.0     1.6.2     wheel
    requests           2.32.3    2.34.2    wheel
    soupsieve          2.6       2.9       wheel
    urllib3            2.3.0     2.7.0     wheel

The simplest way to update all these packages in one go was to install pip-review, a helper for Python's pip package installer. We can update everything in one go with the auto parameter.

    pip install pip-review
    pip-review --auto

Using older Python versions in a virtual environment

If you want to or need to use a different python version you have to install it first on your linux system and use then the right command (e.g. python3.9):

    sudo apt install python3.9
    mkdir /savit/programming/python/test
    python3.9 -m venv /savit/programming/python/test

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