Document what happens when venv is run using existing directory

Documentation

Please consider specifying the behavior of venv module when the ENV_DIR already exists, and/or is not empty and/or contains an existing virtual environment. Currently the docs mentions only: “running this command creates the target directory”, and “creates” implies the command should be executed when ENV_DIR is not present [1].

However, I am able to run python -m venv .venv twice, and there is no error. There is no mention in the docs what happens when the directory is already there. Does venv skips creation of virtual environment? Does it try to create it anyways? What if ENV_DIR content is already a virtual environment? What if it is somewhat broken, does venv try to “fix” it?

[1] On the other hand, there are options --clear, --update, --update-deps, and those imply the ENV_DIR should be present. But it contradicts the previous assumption.

Linked PRs

• gh-151419

檢視 venv 模組文件和連結的 PR gh-151419，然後將其中的措辭與針對現有、非空、有效及損壞的 ENV_DIR 目錄執行 python -m venv 時的行為進行比較。完成標準是文件說明這些行為，以及 --clear、--update 和 --update-deps 如何影響這些行為。