Activation

Activation puts the environment’s binary directory at the front of PATH and records the environment in VIRTUAL_ENV, so python and pip resolve to the environment without any absolute paths. tn-venv generates scripts for seven activation mechanisms in one pass.

Generated scripts

File	Shell	Activation command
activate	bash, zsh, and other POSIX sh	source <env>/bin/activate
activate.bat	cmd.exe	<env>\Scripts\activate.bat
deactivate.bat	cmd.exe	deactivate.bat
Activate.ps1	PowerShell / pwsh	<env>\Scripts\Activate.ps1
activate.fish	fish	source <env>/bin/activate.fish
activate.csh	csh, tcsh	source <env>/bin/activate.csh
activate.nu	Nushell	overlay use <env>/bin/activate.nu
activate_this.py	no shell — in-process	see below

On Windows the environment directory is Scripts; elsewhere it is bin. activate.bat and deactivate.bat are only generated on Windows; every other script is generated on every platform.

All scripts share the same semantics:

1. VIRTUAL_ENV is set to the environment directory and exported.

2. The environment’s binary directory is prepended to PATH; the previous value is stashed so deactivate can restore it exactly.

3. PYTHONHOME is unset if set (and restored by deactivate).

4. Unless VIRTUAL_ENV_DISABLE_PROMPT is non-empty, the shell prompt is prefixed with (<prompt>) and VIRTUAL_ENV_PROMPT is set.

5. deactivate (a shell function, or deactivate.bat on cmd) reverses all of the above, including restoring the previous prompt.

Nested activation is safe: activating environment B while A is active stacks the changes, and deactivate returns to A’s state.

Choosing which scripts to generate

$ tn-venv .venv --activators powershell,batch
$ tn-venv .venv --activators all
$ tn-venv .venv --activators default,-nushell,-csh

The value is comma-separated and repeatable. Accepted names are bash, batch, powershell, fish, csh, nushell, python, plus the two pseudo-names all and default. A leading - removes a name from the default set. Unknown names are rejected with exit code 2 and the list of valid names.

The prompt

By default the prompt is the environment’s folder name. Override it with:

$ tn-venv .venv --prompt "api-dev"

A custom prompt is also recorded in pyvenv.cfg (see pyvenv.cfg reference), which is how python -m venv --upgrade learns to keep it. To suppress prompt modification at activation time, without changing the scripts, set VIRTUAL_ENV_DISABLE_PROMPT to any non-empty value before sourcing.

activate_this.py

activate_this.py activates an environment inside an already-running Python process — the classic virtualenv mechanism, kept for compatibility with embedding tools and long-lived application servers:

activate_this = "/path/to/.venv/bin/activate_this.py"
with open(activate_this) as f:
    code = compile(f.read(), activate_this, "exec")
    exec(code, {"__file__": activate_this})

It prepends the environment’s binary directory to PATH, sets VIRTUAL_ENV and VIRTUAL_ENV_PROMPT, adds the environment’s site-packages via site.addsitedir(), and rewrites sys.prefix (keeping the old value in sys.real_prefix). It cannot un-import already-loaded modules, so it is only safe to use early in a process’s lifetime.

Warning

On POSIX systems the POSIX-shell script must be sourced, not executed: source .venv/bin/activate. Executing it in a subshell activates the subshell only and is silently useless — the scripts detect nothing; this is inherent to how shells work, not a tn-venv limitation.