How to use virtual environments
Why isolate dependencies
Different projects may require different package versions. A virtual environment gives a project its own Python executable and installed packages without changing the system Python.
mkdir weather-app
cd weather-app
python3 -m venv .venvActivate the environment
Activation places the environment's executables first on PATH. The prompt often shows (.venv).
# macOS/Linux:
source .venv/bin/activate
# Windows Command Prompt:
.venv\Scripts\activate.bat
# Windows PowerShell:
.venv\Scripts\Activate.ps1Install and verify
After activation, installs go into the environment. Confirm which interpreter is active before installing.
python --version
python -m pip install requests
python -m pip show requestsLeave and recreate
Run deactivate to leave. Do not commit .venv; record dependencies and recreate the environment instead.
python -m pip freeze > requirements.txt
deactivate
# Later:
python3 -m venv .venv
# activate, then:
python -m pip install -r requirements.txt