Installing Python on Windows with pyenv

We are going to install pyenv-win, a small tool to install Python releases and switch between versions of the interpreter. Following the instructions from the web, we will open a PowerShell window and type

Invoke-WebRequest -UseBasicParsing -Uri "https://raw.githubusercontent.com/pyenv-win/pyenv-win/master/pyenv-win/install-pyenv-win.ps1" -OutFile "./install-pyenv-win.ps1"; &"./install-pyenv-win.ps1"
rm install-pyenv-win.ps1

Close the terminal and open it again to have access to the new tool. You can verify that the tool is installed

C:\Users\user>pyenv
pyenv 3.1.1

Usage: pyenv <command> [<args>]

Some useful pyenv commands are:
   commands     List all available pyenv commands
   duplicate    Creates a duplicate python environment
   local        Set or show the local application-specific Python version
   global       Set or show the global Python version
   shell        Set or show the shell-specific Python version
   install      Install a Python version using python-build
   uninstall    Uninstall a specific Python version
   update       Update the cached version DB
   rehash       Rehash pyenv shims (run this after installing executables)
   vname        Show the current Python version
   version      Show the current Python version and its origin
   version-name Show the current Python version
   versions     List all Python versions available to pyenv
   exec         Runs an executable by first preparing PATH so that the selected Python
   which        Display the full path to an executable
   whence       List all Python versions that contain the given executable

See `pyenv help <command>' for information on a specific command.
For full documentation, see: https://github.com/pyenv-win/pyenv-win#readme

Run pyenv update and then install one version of the interpreter. You may look at the Python download page to see which versions are available with which levels of maturity, but first also confirm that the version is available with pyenv install -l. In my case I chose 3.10.11 which is the last version with a security maintenance status, setting it also as a the global version of python to use

pyenv install --quiet 3.10.11
pyenv global 3.10.11

After this, we can check it works

> pyenv version
3.10.11 (set by C:\Users\juanj\.pyenv\pyenv-win\version)
> python -c "import sys; print(sys.executable)"
C:\Users\juanj\.pyenv\pyenv-win\versions\3.10.11\python.exe

When working with python software, it is customary to create a unique environment that contains only the libraries and tools the software needs. This allows you as a developer to keep track of the requirements of your software and which versions of the libraries are used, making the process more reproducible for other users and for yourself, should you move to a different computer.

Assuming you have set up a new Python project in the folder c:\Users\me\src\myproject, what you would do now is to use your pyenv installation to create a fresh new environment in that particular folder

> cd c:\Users\me\src\myproject
> python -m venv .venv

This creates a subfolder, with name .venv that contains a link to a particular version of python and the pip tool to install the software.

You can activate this software from the command line. When using the Windows command line processor this looks as follows:

C:\Users\me\src\myproject>.venv\Scripts\activate.bat
(.venv) C:\Users\me\src\myproject> python -c "import sys; print(sys.executable)"
C:\Users\me\src\myproject\.venv\Scripts\python.exe

When using PowerShell it changes a bit:

PS C:\Users\me\src\myproject> & c:/Users/me/src/myproject/.venv/Scripts/Activate.ps1
(.venv) PS C:\Users\me\src\myproject> python -c "import sys; print(sys.executable)"
C:\Users\me\src\myproject\.venv\Scripts\python.exe

Note how in both cases the current environment (.venv) appears at the beginning of the prompt, indicating where our Python software is installed.

Now it is the time to install whatever libraries your software needs. Ideally, you should create a requirements.txt file, with a list of the libraries, which in my case would read

numpy
scipy
matplotlib

and then install it using pip

(.venv) PS C:\Users\me\src\myproject> pip install -r requirements.xt

I personally recommend using Visual Studio Code as a development environment for Python on Windows, for various reasons:

1. Once you install this editor and open a Python file (with extension .py), it will suggest to install the editor's tools for handling Python as a language, including syntax verifiers and Pylance as language server to autocomplete and verify the code.
2. If you have created a Python environment local to your project, as explained above, you can select this environment to check, test and run your software.
3. If you tell VS Code to use other Python tools, such as autoformatting with black, or opening Jupyter Notebooks, the editor will upgrade your Python environment with additional tools to handle those tasks transparently.