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What is a Virtual Environment?

There are many versions of Python and many packages that can be installed, each with its own dependencies on specific versions of other packages. A single Python installation can get problematic if different installed packages depend on different versions of the same package, and such dependency conflicts can cause bugs and even prevent certain packages (like MPF) from running properly.

A "virtual environment" is a way to create an isolated, sandboxed environment for a specific Python version. Packages installed in this environment are separate from packages installed in other environments, including their dependencies.

It is highly recommended to install MPF in a virtual environment.

In fact, current releases of Debian (12) and Ubuntu (23) do not allow Python packages to be installed outside of a virtual environment, so on those platforms a virtual environment is required.

Create a Virtual Environment

To create a virtual enviroment, choose a folder where you want to install a copy of Python and keep the enviroment's packages. For this example, we'll call the environment "mpfenv" and put it in our home directory (known as "~").

  python3 -m venv ~/mpfenv

Or if you want to explicitly define a directory, like this example of an "mpf" virtual environment in a common venvs directory (because remember you can have as many virtual environments as you like):

  python3 -m venv C:\Users\Rudy\venvs\mpf

Note

If you have multiple versions of Python3 (say, 3.9 and 3.11), you can specify which one to use in the virtual environment: python3.9 -m venv ~/mpfenv

A virtual environment is recommended for any general-use computer you'll be using MPF on. For a dedicated MPF machine that will have no other programs installed (for example, a computer inside a pinball cabinet), a virtual environment is not required (except see above note regarding Debian and Ubuntu) but can still be helpful for keeping packages organized and cleanly upgrading.

Activate your Virtual Environment

To keep itself isolated from other programs, your virtual enviroment only activates when you tell it to. You can enable the virtual environment with the dot command from the terminal:

  . ~/mpfenv/bin/activate

Note that the first character is a period, followed by a space, then the path to your virtual environment and "/bin/activate".

For Windows users, you well activate with a bat/ps1 script depending on whether you're using the Command Prompt or the PowerShell.

# Command Prompt:
> mpfenv/Scripts/activate.bat

# PowerShell:
PS > mpfenv/Scripts/Activate.ps1

For users on Mac OSX, you will use source instead:

  source ~/mpfenv/bin/activate

Note

You may want to write this step down, as you'll run it every time you open up a terminal window to work on MPF. If you are on a dedicated MPF machine, you could add this line to your bash/zsh profile to automatically run it at login.

You'll know you're in the virtual environment because the console prompt will include the name of your venv in parenthesis.

  My-Mac:~ python --version
  Python 2.7.10
  My-Mac:~ source ~/mpfenv/bin/activate
  (mpfenv) My-Mac:~ python --version
  Python 3.9.13
  (mpfenv) My-Mac:~

python

The python you used to create the virtual environment will now be the default python. Outside the virtual environment "python" may be Python 2 or 3, and "python3" may be 3.6 or 3.9 or 3.11; inside the virtual environment, you can use "python" to refer to the exact version of Python 3 you used to create the virtual environment

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