python - 虚拟环境下python 3.8如何构造sys.path？

Question

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

.
├── 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，mmdetection与qd-track处于同一级别的 和，被、while和py38weren 拾取。我将名称更改为，并创建了几个新的空文件夹, ，这使当前文件夹看起来像：sys.pathmonodepth2py37mmdetectionmmdetection2detectrondetectron2

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

然后我尝试再次打印 sys.path ，并得到：

(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没有被捡起来detectron。这太奇怪了，因为路径似乎是由 python 动态检测到的，而不是从某些固定索引中读取的。究竟如何检测它们让我感到困惑。我检查PYTHONPATH了，它是空的。

更有趣的是，我尝试切换到与py37并排放置的环境，但py38没有发生上述任何情况：

(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']

那么，我想这可能是由于从 python3.8 开始对加载机制的一些新变化？而且，当我使用 sys.path 时，我应该期待什么行为？官方文档没有给出要包含在 sys.path 中的项目的确切列表。

顺便说一句，我使用的是 Ubuntu 18.04.3 LTS；py37并py38通过 virtualenv 创建。

标签： pythonpython-3.xvirtualenvsys.path