zsh: command not found: virtualenv

zsh: command not found: virtualenv means the virtualenv command is not in any directory on your PATH. virtualenv is a third-party package; Python does not include it. Python 3 does include venv, which covers what most people need:

python3 -m venv .venv
source .venv/bin/activate
python --version

Inside the activated environment python and pip point at the project's copy. Run deactivate to leave. If that is all you wanted, you are done.

zsh: command not found: python

macOS has no python command; Apple removed Python 2 in macOS 12.3 and never added a python alias for Python 3. Use python3. Inside an activated venv, python works again because the venv provides it.

When you really need virtualenv

Some tools and older guides call virtualenv directly, and it has features venv lacks, such as creating environments for other Python versions. How to install it depends on which Python you have.

Homebrew Python: pip refuses with externally-managed-environment

pip3 install virtualenv
# error: externally-managed-environment

Homebrew marks its Python as managed by Homebrew (PEP 668), so pip will not install packages into it. Do not add --break-system-packages. Install the command with Homebrew or pipx instead:

brew install virtualenv
# or
brew install pipx
pipx ensurepath
pipx install virtualenv

pipx ensurepath adds ~/.local/bin to your shell startup files. Open a new terminal tab afterwards.

Apple's python3: the script is installed in ~/Library/Python

The python3 that comes with the Xcode Command Line Tools lets you install with pip3 install --user virtualenv. pip then prints a warning that is easy to miss:

WARNING: The script virtualenv is installed in
'/Users/you/Library/Python/3.9/bin' which is not on PATH.

That folder is the reason zsh cannot find the command. Either call it through Python, which needs no PATH change:

python3 -m virtualenv .venv

or add the folder from the warning to ~/.zprofile, using the version number pip printed:

export PATH="$HOME/Library/Python/3.9/bin:$PATH"

To find the folder without the warning, run python3 -m site --user-base and add /bin.

pyenv virtualenv and mkvirtualenv

Two similar errors come from add-ons rather than from virtualenv itself:

pyenv: no such command `virtualenv' means the pyenv-virtualenv plugin is not installed or not loaded. Install it with brew install pyenv-virtualenv and add eval "$(pyenv virtualenv-init -)" to ~/.zshrc after the pyenv init line.
zsh: command not found: mkvirtualenv comes from virtualenvwrapper. Its commands are shell functions, so installing the package is not enough: your ~/.zshrc must source the virtualenvwrapper.sh script, as its documentation describes.

Check where things are

command -v python3 pip3 virtualenv pipx
print -l $path

If a tool is installed but its folder is missing from the list, the fix is a PATH line in the right startup file. zsh: command not found on macOS: how PATH works covers which file to edit and why.