Why should I use a virtual environment?

A virtual environment is an isolated Python runtime environment that allows you to work on different Python projects with different dependencies without conflicts. Understanding virtual environments is fundamental to effective Python development.

The Problem Virtual Environments Solve

When you install Python packages globally (directly into your system Python), several problems can arise:

• Version conflicts: Different projects might need different versions of the same package
• Dependency pollution: Installing packages globally makes it hard to track which packages are actually needed for each project
• System integrity: Modifying system Python packages can break system tools that depend on specific versions
• Reproducibility: Without isolation, it’s difficult to ensure your project works the same way on different machines

Virtual environments solve these problems by creating isolated spaces where each project can have its own independent set of packages and even its own Python version.

How Virtual Environments Work

A virtual environment is primarily a directory containing a Python installation or symlinks to one, along with a site-packages directory for installing dependencies. When activated, it modifies your shell’s PATH to use this isolated environment instead of your system Python.

Key aspects of virtual environments:

• They can use different Python versions
• Each has its own package registry (site-packages directory)
• They don’t copy all Python files - they use symlinks to be efficient
• They can be easily created and destroyed without affecting other environments
• They can be recreated from requirement specifications

Modern Virtual Environment Management

While tools like venv and virtualenv have traditionally been used to create virtual environments, modern tools like uv handle virtual environment management automatically:

• uv creates environments on demand
• Dependencies are installed into the environment automatically
• Project environments are activated implicitly when running commands
• Environments are kept in sync with project requirements

Best Practices

When working with virtual environments:

• Use one environment per project: Don’t try to share environments between projects
• Don’t version control environments: Add .venv to your .gitignore
• Keep environments disposable: Be able to recreate them from requirements
• Use project-local environments: Store them in your project directory (typically as .venv)