On Windows Powershell, venv folders are unexpectedly importable due to how namespace package and venv works

Bug report

PEP420 introduced implicit namespace package, basically by creating a folder without __init__.py, it is treated as namespace package.

For some reasons, in Windows Powershell, venv added the environment's root folder into sys.path (this behavior was not observed in Linux's venv), e.g.

PS C:\Users\TestUser> python -m venv testenv
PS C:\Users\TestUser> . .\testenv\Scripts\activate
(testenv) PS C:\Users\TestUser> python
Python 3.10.5 (tags/v3.10.5:f377153, Jun  6 2022, 16:14:13) [MSC v.1929 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.path
[
    [snip] 
    'C:\\Users\\TestUser\\testenv', 
    'C:\\Users\\TestUser\\testenv\\lib\\site-packages'
]

And because of the way namespace package works, you can import some folders that really aren't intended to be importable:

>>> import Include
>>> Include.__path__
_NamespacePath(['C:\\Users\\TestUser\\testenv\\Include'])
>>>

This was a namespace package created from the Include folder in the root of the testvenv folder:

PS C:\Users\TestUser> ls .\testenv\


    Directory: C:\Users\TestUser\testenv


Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d-----         7/18/2022   1:15 PM                Include
d-----         7/18/2022   1:15 PM                Lib
d-----         7/18/2022   1:15 PM                Scripts
-a----         7/18/2022   1:15 PM            127 pyvenv.cfg

Similarly, you could have imported Lib and Scripts.

Your environment

Python 3.10.5 (tags/v3.10.5:f377153, Jun 6 2022, 16:14:13) [MSC v.1929 64 bit (AMD64)] on win32

首先重現報告中的 Windows PowerShell 命令，並在建立及啟用 venv 後檢查 sys.path。比較 Windows 和 Linux 上 venv 的行為，然後判斷 Include、Lib 和 Scripts 目錄如何變得可匯入。當不再能夠匯入非預期的 venv 目錄，同時又不會破壞正常的環境匯入時，即表示完成。