UV Python Version Management

Quick reference for installing and managing Python interpreter versions with UV.

When to Use This Skill

When This Skill Applies

• Installing specific Python versions
• Switching between multiple Python versions
• Pinning Python versions for projects
• Managing CPython and PyPy interpreters
• Finding and listing installed Python versions

Quick Reference

Installing Python Versions

# Install latest Python
uv python install

# Install specific version
uv python install 3.11
uv python install 3.12
uv python install 3.10 3.11 3.12

# Install exact version
uv python install 3.11.5
uv python install cpython@3.11.5

# Install PyPy
uv python install pypy@3.9
uv python install pypy@3.10

Listing Python Versions

# List all available versions
uv python list

# List only installed versions
uv python list --only-installed

# List with verbose details
uv python list --verbose

Pinning Python Versions

# Pin version for current project
uv python pin 3.11
uv python pin 3.12.1

# Pin PyPy
uv python pin pypy@3.9

# Pin with version file
# Creates/updates .python-version

Finding Python Interpreters

# Find any Python installation
uv python find

# Find specific version
uv python find 3.11
uv python find 3.12

# Find PyPy
uv python find pypy
uv python find pypy@3.9

Using Specific Python Versions

# In project commands
uv run --python 3.11 script.py
uv run --python 3.12 pytest

# Creating virtual environments
uv venv --python 3.11
uv venv --python 3.10 .venv-py310

# Initializing projects
uv init --python 3.12 my-project

Python Version Sources

UV searches for Python in this order:

1. UV-managed - Installed via uv python install
2. .python-version - Pin file in project directory
3. pyproject.toml - requires-python field
4. System Python - Existing system installations
5. Environment - $PATH and standard locations

Version Pinning

.python-version File

# Pin creates this file
uv python pin 3.11

# File contents
3.11

# Exact version
uv python pin 3.11.5

pyproject.toml

[project]
requires-python = ">=3.11"

# UV respects this constraint

Supported Python Implementations

CPython

# Default implementation
uv python install 3.11
uv python install cpython@3.11
uv python install cpython@3.11.5

PyPy

# Alternative Python implementation
uv python install pypy@3.9
uv python install pypy@3.10

Common Commands

# Install and pin latest Python 3.12
uv python install 3.12 && uv python pin 3.12

# Install multiple versions for testing
uv python install 3.10 3.11 3.12

# Check which Python is active
uv python find
uv run python --version

# Uninstall version (manual)
rm -rf ~/.local/share/uv/python/cpython-3.11.5-*

Integration with Projects

Project Initialization

# Initialize with specific Python
uv init --python 3.11 my-project

# Generates .python-version
cat .python-version
# 3.11

Running Commands

# Use project's pinned Python
uv run python script.py

# Override with specific version
uv run --python 3.12 script.py

# Use system Python
uv run --python python3 script.py

Multi-Version Testing

# Test across Python versions
uv run --python 3.10 pytest
uv run --python 3.11 pytest
uv run --python 3.12 pytest

# Create version-specific venvs
uv venv --python 3.10 .venv-py310
uv venv --python 3.11 .venv-py311
uv venv --python 3.12 .venv-py312

Key Features

• Fast downloads: Parallel downloads with caching
• Automatic: Downloads versions on-demand
• Isolated: UV-managed versions don't conflict with system Python
• Portable: Uses standalone Python distributions
• Cross-platform: Works on Linux, macOS, and Windows

See Also

• uv-project-management - Using pinned Python versions in projects
• uv-workspaces - Python versions in monorepos
• python-testing - Testing across multiple Python versions

References

• Official docs: https://docs.astral.sh/uv/guides/install-python/
• Python standalone builds: https://github.com/indygreg/python-build-standalone
• Detailed guide: See REFERENCE.md in this skill directory