Python venv: 'source: venv/bin/activate: No such file or directory' on Windows, or 'venv\Scripts\activate is not recognized' on Linux/macOS. How do I activate a virtual environment on each platform (and in CI)?

Cause: virtual environments use different folder layouts per platform. On Linux and macOS the scripts live in <venv>/bin; on Windows they live in <venv>\Scripts. Each shell also needs its own activation script. Copying an activation command from a tutorial written for another OS, using Git Bash or WSL against a venv created by Windows Python (or the reverse), or moving/copying a venv folder (venvs aren't relocatable) produces 'No such file or directory' or 'not recognized' errors. Fix: 1. Activate with the script for your OS and shell (the venv docs list them): - Linux/macOS bash or zsh: source .venv/bin/activate - fish: source .venv/bin/activate.fish - Windows cmd: .venv\Scripts\activate.bat - Windows PowerShell: .venv\Scripts\Activate.ps1 (if blocked, see PowerShell execution policy: Set-ExecutionPolicy RemoteSigned -Scope CurrentUser) - Git Bash on Windows: source .venv/Scripts/activate 2. Create the venv with the same Python you'll run it with: a venv made by Windows Python can't be used from WSL's Linux Python and vice versa; make a separate one in each environment. 3. Don't move or copy a venv to another path or machine; delete it and recreate it there (python -m venv .venv, then pip install -r requirements.txt). 4. You don't have to activate at all: run the venv's interpreter directly, which is the most reliable option in scripts, cron and CI: .venv/bin/python app.py (Windows: .venv\Scripts\python.exe app.py), and .venv/bin/python -m pip install ... . 5. In CI, each step usually runs in a new shell, so activation doesn't carry over; call the venv's python by path, or put its bin/Scripts folder at the front of PATH for later steps. Verify: python -c "import sys; print(sys.prefix)" prints the venv's path (it differs from sys.base_prefix inside a venv). Sources: https://docs.python.org/3/library/venv.html https://packaging.python.org/en/latest/guides/installing-using-pip-and-virtual-environments/