如何创建仅包含一个版本的 python/pip 的 python 虚拟环境？

Question

I had been under the impression that if I created a python environment with a specific python version, it would use just that version, but it seems I was mistaken:

$ /usr/bin/python3 -m venv pyenv
$ ls pyenv
$ ls pyenv/bin
activate      activate.fish  easy_install      pip   pip3.8  python3
activate.csh  Activate.ps1   easy_install-3.8  pip3  python

Is there any reason why older versions of python need to exist alongside the current one in my venv? And can I specify not to, or should I just manually delete the python2/pip?

Answer 1

In your virtual environment, all the python* executables will point to the same version. You can see this from the symbolic links:

$ /usr/bin/python3 -m venv pyenv

$ cd pyenv/bin

$ ls -l python*
lrwxrwxrwx 1 [user] [group]  7 May 28 05:49 python -> python3
lrwxrwxrwx 1 [user] [group] 16 May 28 05:49 python3 -> /usr/bin/python3

Similarly all the pip executables will be copies of the same file:

$ ls -l pip*
-rwxr-xr-x 1 [user] [group] 212 May 28 05:49 pip
-rwxr-xr-x 1 [user] [group] 212 May 28 05:49 pip3
-rwxr-xr-x 1 [user] [group] 212 May 28 05:49 pip3.6

$ diff3 pip*
[no output]

This means, for example, that once you have run the activate script so that this bin directory is in your PATH , you will find the python in your virtual environment regardless of whether you type python or python3 .

The same is true of python scripts which you invoke with #!/usr/bin/env python or #!/usr/bin/env python3 for example.

Only if you explicitly invoke a different version of python (for example python2 ) or give a full path to the python executable (for example /usr/bin/python ) might you find another version located elsewhere on your system.