Python Environments Cheatsheet

venv (standard library)

python3 -m venv .venv

Creates a virtual environment in a .venv folder, isolated from your system Python.

source .venv/bin/activate

Activates the environment on Linux/macOS - your shell prompt changes to show it’s active.

.venv\Scripts\Activate.ps1

Activates the environment on Windows PowerShell.

deactivate

Exits the active virtual environment, returning to your system Python.

which python

Confirms which python binary is currently active (should point inside .venv once activated).

pip

pip install requests

Installs a package into the currently active environment.

pip install requests==2.32.3

Installs an exact, pinned version.

pip install -r requirements.txt

Installs every package listed in a requirements file.

pip freeze > requirements.txt

Writes every currently installed package and its exact version to a requirements file.

pip list --outdated

Lists installed packages that have a newer version available.

pip install --upgrade requests

Upgrades a single package to its latest compatible version.

pip uninstall requests

Removes a package from the environment.

pip show requests

Shows a package’s version, location, and dependencies.

pip install -e .

Installs the current project in “editable” mode, so code changes take effect without reinstalling.

pipx (for CLI tools)

pipx install black

Installs a Python CLI tool into its own isolated environment, exposing only its command globally.

pipx list

Lists tools installed via pipx.

pipx upgrade black

Upgrades a pipx-installed tool.

pipx run black --check .

Runs a tool once without permanently installing it.

pyenv (multiple Python versions)

pyenv install 3.12.6

Downloads and builds a specific Python version.

pyenv versions

Lists Python versions installed via pyenv.

pyenv global 3.12.6

Sets the default Python version for your whole user account.

pyenv local 3.11.9

Pins a Python version for the current project, writing a .python-version file.

pyenv which python

Shows the full path to the Python binary pyenv would currently run.

Poetry

poetry init

Interactively creates a pyproject.toml for a new project.

poetry add requests

Adds a dependency and installs it into a Poetry-managed virtual environment.

poetry add --group dev pytest

Adds a dependency to a specific group (e.g. dev-only tools), keeping it out of production installs.

poetry install

Installs all dependencies listed in pyproject.toml/poetry.lock.

poetry remove requests

Removes a dependency from the project.

poetry run python app.py

Runs a command inside the project’s virtual environment without manually activating it.

poetry shell

Opens an interactive shell with the project’s virtual environment activated.

poetry update

Updates dependencies to the latest versions allowed by pyproject.toml, rewriting the lockfile.

poetry export -f requirements.txt -o requirements.txt

Exports a requirements.txt from poetry.lock, for tools that expect the plain-pip format.

uv (fast, modern tooling)

uv venv

Creates a virtual environment (in .venv by default), much faster than python -m venv.

uv pip install requests

Installs a package using pip-compatible syntax, but with uv’s much faster resolver.

uv pip sync requirements.txt

Installs exactly the packages listed, removing anything not in the file - reproducible installs.

uv init myproject

Scaffolds a new project with a pyproject.toml already set up.

uv add requests

Adds a dependency to the project and updates the lockfile, similar to poetry add.

uv run app.py

Runs a script inside the project’s environment, creating/syncing it automatically first if needed.

uv python install 3.12

Downloads and manages a specific Python version, without needing pyenv.

uv lock

Resolves and writes the project’s lockfile without installing anything.