Manage Multiple Python Versions

To manage multiple Python versions on a Windows machine, you can follow these steps:

• Install Python: First, download and install the different Python versions you want to manage. You can download the installers for each version from the official Python website (https://www.python.org/downloads/windows/).

• Set Environment Variables: During the installation process, make sure to check the option to add Python to the system PATH. This will allow you to access Python from the command line.

• To check the list of all installed Python versions on a Windows machine, you can use the py command with the -0 (zero) option. Open the command prompt and run the following command:

    py -0

• This will display a list of all the installed Python versions along with their respective installation paths. The output will look something like this:

  -V:3.11 *        Python 3.11 (64-bit)

  -V:3.9           Python 3.9 (64-bit)

• In this example, you can see that Python 3.9 and 3.11 are installed, along with their corresponding architecture.

• The Python version marked with an asterisk (*) indicates the default version that will be used when running scripts without specifying a specific version.

• To change the Python version on a Windows machine using the command prompt, you can use the py command with the -3.X option, where X represents the desired Python version number.

Here's how you can change the Python version:

• Open the command prompt.

• Run the following command to switch to a specific Python version:

    py -3.X

• Replace X with the desired Python version number. For example, to switch to Python 3.9, you would run:

    py -3.9

• Once you execute this command, the system will switch to the specified Python version, and any subsequent Python-related commands or scripts you run will use that version.

• You can verify the current Python version by running the command python --version. It should display the version number of the Python interpreter you switched to.

• Note that the py command is designed to manage multiple Python versions on Windows, so it allows you to switch between installed versions easily.

• Python doesn't provide any command to set a specific installed version of Python as the default on a Windows machine. But don't worry, you can create a virtual environment in a specific Python version.

Use Virtual Environments:

• Virtual environments provide a way to isolate Python environments and manage packages separately for different projects. You can use the venv module to create virtual environments. 

• Here are the basic steps to create and activate a virtual environment:

• Open the command prompt and navigate to the project directory.

• Create a virtual environment by running the following command:

    py -3.9 -m venv env

• Activate the virtual environment:

    

    env\Scripts\activate

• You'll notice the prompt changing to indicate that you're working inside the virtual environment.

• Install packages and run your project within the virtual environment.

• By following these steps, you should be able to manage multiple Python versions on your Windows machine effectively.