Python3.8在虚拟环境中如何构造sys.path？

Question

当我检查python3.8虚拟环境中的sys.path时，我注意到一些奇怪的事情。具体来说，我的playground中有以下层次结构：

.
├── mmdetection
├── monodepth2
├── py37
├── py38
└── qd-track

当我调用python环境py38并查看sys.path成员时，我注意到以下模式：

dian@ubuntu:~/playground$ ls
mmdetection  monodepth2  py37  py38  qd-track
dian@ubuntu:~/playground$ source py38/bin/activate
(py38) dian@ubuntu:~/playground$ python
Python 3.8.0 (default, Oct 28 2019, 16:14:01) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.path
['', '/usr/lib/python38.zip', '/usr/lib/python3.8', '/usr/lib/python3.8/lib-dynload', '/home/dian/playground/py38/lib/python3.8/site-packages', '/home/dian/playground/mmdetection', '/home/dian/playground/py38/lib/python3.8/site-packages/terminaltables-3.1.0-py3.8.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/mmpycocotools-12.0.3-py3.8-linux-x86_64.egg', '/home/dian/playground/qd-track', '/home/dian/playground/py38/lib/python3.8/site-packages/motmetrics-1.2.0-py3.8.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/mmcv-1.1.5-py3.8-linux-x86_64.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/xmltodict-0.12.0-py3.8.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/scipy-1.5.3-py3.8-linux-x86_64.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/pytest_benchmark-3.2.3-py3.8.egg']

有趣的是{}和{}在{}的同一水平上，被{}接受，而{}和{}没有。我将mmdetection的名称更改为mmdetection2，并创建了两个新的空文件夹detectron，detectron2，这使当前文件夹看起来像：

.
├── detectron
├── detectron2
├── mmdetection2
├── monodepth2
├── py37
├── py38
└── qd-track

然后我再次尝试打印sys.path，得到：

(py38) dian@ubuntu:~/playground$ python
Python 3.8.0 (default, Oct 28 2019, 16:14:01) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.path
['', '/usr/lib/python38.zip', '/usr/lib/python3.8', '/usr/lib/python3.8/lib-dynload', '/home/dian/playground/py38/lib/python3.8/site-packages', '/home/dian/playground/detectron2', '/home/dian/playground/py38/lib/python3.8/site-packages/terminaltables-3.1.0-py3.8.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/mmpycocotools-12.0.3-py3.8-linux-x86_64.egg', '/home/dian/playground/qd-track', '/home/dian/playground/py38/lib/python3.8/site-packages/motmetrics-1.2.0-py3.8.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/mmcv-1.1.5-py3.8-linux-x86_64.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/xmltodict-0.12.0-py3.8.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/scipy-1.5.3-py3.8-linux-x86_64.egg', '/home/dian/playground/py38/lib/python3.8/site-packages/pytest_benchmark-3.2.3-py3.8.egg']

这一次，mmdetection2消失了，detectron2被拾起，而detectron没有。这太奇怪了，因为路径似乎是由python动态检测的，而不是从某些固定索引读取的。而它们到底是如何被发现的，我感到困惑。我检查了PYTHONPATH，它是空的

更有趣的是，我尝试切换到py37环境，该环境与py38并排放置，但没有发生上述情况：

(py38) dian@ubuntu:~/playground$ deactivate
dian@ubuntu:~/playground$ source py37/bin/activate
(py37) dian@ubuntu:~/playground$ python
Python 3.7.5 (default, Nov  7 2019, 10:50:52) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.path
['', '/usr/lib/python37.zip', '/usr/lib/python3.7', '/usr/lib/python3.7/lib-dynload', '/home/dian/playground/py37/lib/python3.7/site-packages', '/home/dian/playground/py37/lib/python3.7/site-packages/terminaltables-3.1.0-py3.7.egg']

所以，我想这可能是因为从python3.8开始对加载机制进行了一些新的更改？而且，当我使用sys.path时，我应该期望什么样的行为？官方文档没有给出sys.path中要包含的项目的确切列表

顺便说一下，我使用的是Ubuntu 18.04.3 LTSpy37和py38是通过virtualenv创建的