PS1 is exported when a virtual environment is activated

[romkatv]

Bug report

Bug description:

• Expected: When a virtual environment is (de)activated, PS1 is not exported.
• Actual: When a virtual environment is (de)activated, PS1 is exported.

PS1 is an internal shell parameter. Exporting it causes all child processes to inherit it. This becomes a problem if a child process happens to be a shell of another kind (e.g., the parent is bash and the child is zsh), which recognizes PS1 as a special parameter but with incompatible syntax. In general, internal shell parameters should not be exported.

# Create a virtual environment.
bash-5.0$ python3 -m venv .env

# Verify that PS1 is not exported.
bash-5.0$ typeset -p PS1
declare -- PS1="\\s-\\v\\\$ "

# Activate the virtual environment.
bash-5.0$ source .env/bin/activate

# PS1 is now exported. This is unexpected.
(.env) bash-5.0$ typeset -p PS1
declare -x PS1="(.env) \\s-\\v\\\$ "

# Start zsh.
(.env) bash-5.0$ zsh -f
# Observe that prompt is broken because it's from bash.
(.env) \s-\v\$ 

As far as I can tell, removing the two export PS1 lines from .env/bin/activate is enough to fix this issue.

CPython versions tested on:

3.8

Operating systems tested on:

Linux

Linked PRs

• gh-111501: venv: do not export PS1 in activate #105279

[rpigott]

I already tried removing this in #105279. I still hope cpython will reconsider, but I have since chosen to make my own venv script. There's absolutely nothing to a venv beyond an entry to PATH, so it's really not hard to do better than upstream.

If anyone needs a reference, I use [1] which mimics "workon" from virtualenv_wrapper, and replicate the prompt like [2]

[1] https://git.sr.ht/~brocellous/dotfiles/tree/ad05ed7e79953cb0217d335ff14ba32d4d4094e5/item/.local/share/zsh/pyenv/workon
[2] https://git.sr.ht/~brocellous/dotfiles/tree/ad05ed7e79953cb0217d335ff14ba32d4d4094e5/item/.hostconfig/rdtw/zshrc#L4