Python Virtual Environments

Python Virtual Environments#

A Python virtual environment allows you to install third-party packages for testing without affecting your system’s Python installation. Here are two common methods to create Python virtual environments:

  • The built-in venv module

  • The virtualenv package

Python’s venv Library#

To use the venv module, you can run Python with the -m flag, which tells Python to run the specified module. Open a command prompt on Windows or a terminal on macOS or Linux, and type the following:

python -m venv test

This command creates a folder named test in your current directory. To activate the virtual environment, navigate to the test folder and run this command on Linux/macOS:

source bin/activate

You can now install new packages in your virtual environment without affecting your system. When you’re done, deactivate the virtual environment by running the deactivate command.

The virtualenv Package#

The virtualenv package was the original method for creating Python virtual environments. It has some advantages over the venv module:

  • It’s faster.

  • It can create virtual environments for multiple Python versions.

  • It can be upgraded via pip.

To install virtualenv, use pip:

pip install virtualenv

Once installed, create a virtual environment with this command:

virtualenv <FOLDER_NAME>

Virtual Environment for a Specific Version#

To create a virtual environment for a specific Python version, use:

virtualenv -p python3.7 venv

This command won’t work with the venv module. Activating, deactivating, and freezing work the same way as with the venv module.

Pin Your Dependencies#

To make your virtual environments reproducible, you can create a requirements.txt file while your virtual environment is active:

python -m pip freeze > requirements.txt

After working or deleting your venv folder, recreate the same environment with the requirements.txt file:

virtualenv new-venv
source new-venv/bin/activate
python -m pip install -r requirements.txt

For more information, check out these resources:

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