# Virtualenv — Isolated Python Environments for Every Project

> Virtualenv creates lightweight, isolated Python environments with their own site-packages directories, enabling projects to maintain independent dependency sets without conflicting with system packages.

## Install

Save as a script file and run:

# Virtualenv — Isolated Python Environments for Every Project

## Quick Use
```bash
pip install virtualenv
virtualenv venv
source venv/bin/activate
pip install requests
```

## Introduction
Virtualenv is a tool for creating isolated Python environments. Each environment gets its own Python binary and site-packages directory, allowing different projects to use different package versions without interference. It is the foundational isolation tool that predates and inspired Python's built-in `venv` module.

## What Virtualenv Does
- Creates self-contained Python environments with isolated package directories
- Supports creating environments for different Python interpreter versions
- Provides activation scripts for bash, zsh, fish, PowerShell, and cmd.exe
- Installs pip and setuptools into each environment automatically
- Works on Linux, macOS, and Windows with consistent behavior

## Architecture Overview
Virtualenv creates a new directory structure containing a copy or symlink of the Python interpreter, a fresh `site-packages` directory, and shell activation scripts. When activated, the environment prepends its `bin` directory to PATH so that `python` and `pip` resolve to the environment's copies. Package installations go into the environment's site-packages, completely isolated from the system Python.

## Self-Hosting & Configuration
- Install via pip: `pip install virtualenv` or use pipx: `pipx install virtualenv`
- Create an environment: `virtualenv myenv` (uses the current Python by default)
- Specify a Python version: `virtualenv -p python3.11 myenv`
- Activate on Unix: `source myenv/bin/activate`; on Windows: `myenvScriptsactivate`
- Configure defaults in `virtualenv.ini` or via environment variables like `VIRTUALENV_PYTHON`

## Key Features
- Faster environment creation than the built-in venv module with seed package caching
- Support for creating environments with Python versions different from the system default
- Extensible via plugins for custom app-data directories and seed mechanisms
- Discovery mechanism to locate Python interpreters across the system
- Built-in support for creating environments without pip using `--no-pip` for minimal setups

## Comparison with Similar Tools
- **venv (stdlib)** — Built into Python 3.3+; virtualenv is faster, more configurable, and supports more Python versions
- **conda** — Full package and environment manager for multiple languages; virtualenv is Python-only and pip-based
- **Poetry** — Dependency manager that creates virtualenvs internally; virtualenv is the standalone environment tool
- **pipenv** — Combines Pipfile dependency management with virtualenv; virtualenv handles isolation only
- **uv** — Ultra-fast Rust-based Python installer that includes virtualenv creation; virtualenv is the established pure-Python tool

## FAQ
**Q: Should I use virtualenv or the built-in venv module?**
A: Virtualenv is faster, supports more Python versions, and has richer configuration. Use venv when you need zero external dependencies and basic isolation is sufficient.

**Q: Can I create environments for Python versions not installed system-wide?**
A: Virtualenv discovers available Python interpreters but cannot install new ones. Use pyenv or similar tools to install additional Python versions first.

**Q: How do I delete a virtual environment?**
A: Deactivate it with `deactivate`, then delete the directory: `rm -rf myenv`.

**Q: Does virtualenv work with Python 2?**
A: Virtualenv version 20+ requires Python 3.7+ to run but can create environments for Python 2.7 if the interpreter is available on the system.

## Sources
- https://github.com/pypa/virtualenv
- https://virtualenv.pypa.io/

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Source: https://tokrepo.com/en/workflows/asset-83d65337
Author: Script Depot