venv vs virtualenv: Which Python Isolation?
venv ships with the Python standard library; virtualenv is a faster, more featureful third-party tool that also supports older Pythons.
venv is built into Python 3.3+ and is the default way to create isolated environments with no extra install. virtualenv predates it, creates environments faster, supports Python 2 and older 3.x, and offers more configuration and a plugin system. For modern projects on a single recent Python, venv is enough; virtualenv earns its keep for speed, legacy versions, or advanced features.
| venv | virtualenv | |
|---|---|---|
| Bundled | Yes (stdlib) | pip install |
| Speed | Good | Faster creation |
| Python versions | 3.3+ | 2.7 and 3.x |
| Features | Minimal | More options, plugins |
| Best for | Modern single-version | Speed, legacy, power use |
In CI
venv needs nothing extra and works everywhere modern Python runs, so it is the simplest CI choice. virtualenv creates environments a bit faster and is required only if you target old Pythons or want its extra features. Most pipelines use venv and never notice the difference.
Speed it up
Cache the dependency install (pip cache + lockfile) rather than the environment directory itself. Either tool runs on CI runners; faster managed runners shorten install and test steps.
The verdict
Modern projects on a recent Python: venv, since it is built in and needs nothing extra. virtualenv when you need faster creation, support for Python 2 or old 3.x, or its richer feature set. For most teams venv is the simpler default.