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python - 切换 Homebrew 安装的 Python 版本（3.9 → 3.8）

问题描述

这是与此处描述的非常相似的情况，反之亦然。我通过 Homebrew 安装了 Python 3.8 并将其更新为 3.9：

% brew list --formula | grep python
python@3.8
python@3.9

我想使用 Python 3.8 作为我的默认版本，并尝试了 - 受此答案python3的启发- 以下内容：

brew unlink python@3.9
brew unlink python@3.8
brew link python@3.8

最后给了我以下输出：

% brew link python@3.8
Linking /usr/local/Cellar/python@3.8/3.8.6_2... 
Error: Could not symlink bin/pip3
Target /usr/local/bin/pip3
already exists. You may want to remove it:
  rm '/usr/local/bin/pip3'

To force the link and overwrite all conflicting files:
  brew link --overwrite python@3.8

To list all files that would be deleted:
  brew link --overwrite --dry-run python@3.8

所以我做了：

% brew link --overwrite --dry-run python@3.8
Would remove:
/usr/local/bin/pip3

If you need to have this software first in your PATH instead consider running:
  echo 'export PATH="/usr/local/opt/python@3.8/bin:$PATH"' >> ~/.zshrc

我认为先检查一下是个好主意：

ralf@razbook ~ % brew link --force --dry-run python@3.8
Would link:
/usr/local/bin/2to3
/usr/local/bin/2to3-3.8
/usr/local/bin/easy_install-3.8
/usr/local/bin/idle3
/usr/local/bin/idle3.8
/usr/local/bin/pip3
/usr/local/bin/pip3.8
/usr/local/bin/pydoc3
/usr/local/bin/pydoc3.8
/usr/local/bin/python3
/usr/local/bin/python3-config
/usr/local/bin/python3.8
/usr/local/bin/python3.8-config
/usr/local/bin/wheel3
/usr/local/share/man/man1/python3.1
/usr/local/share/man/man1/python3.8.1
/usr/local/lib/pkgconfig/python-3.8-embed.pc
/usr/local/lib/pkgconfig/python-3.8.pc
/usr/local/lib/pkgconfig/python3-embed.pc
/usr/local/lib/pkgconfig/python3.pc
/usr/local/Frameworks/Python.framework/Headers
/usr/local/Frameworks/Python.framework/Python
/usr/local/Frameworks/Python.framework/Resources
/usr/local/Frameworks/Python.framework/Versions/3.8
/usr/local/Frameworks/Python.framework/Versions/Current

If you need to have this software first in your PATH instead consider running:
  echo 'export PATH="/usr/local/opt/python@3.8/bin:$PATH"' >> ~/.zshrc

听起来不错，所以让我们这样做：

 % brew link --force python@3.8 
Linking /usr/local/Cellar/python@3.8/3.8.6_2... 
Error: Could not symlink bin/pip3
Target /usr/local/bin/pip3
already exists. You may want to remove it:
  rm '/usr/local/bin/pip3'

To force the link and overwrite all conflicting files:
  brew link --overwrite python@3.8

To list all files that would be deleted:
  brew link --overwrite --dry-run python@3.8

不幸的是，我跳过了试运行：

 % brew link --overwrite python@3.8
Linking /usr/local/Cellar/python@3.8/3.8.6_2... 25 symlinks created

If you need to have this software first in your PATH instead consider running:
  echo 'export PATH="/usr/local/opt/python@3.8/bin:$PATH"' >> ~/.zshrc

有些东西似乎奏效了：

% python3 --version
Python 3.8.6
% pip3 --version
pip 20.2.4 from /usr/local/lib/python3.8/site-packages/pip (python 3.8)

但还是有pipenv问题：

% pipenv install google-ads
Warning: Python 3.9 was not found on your system...
Neither 'pyenv' nor 'asdf' could be found to install Python.
You can specify specific versions of Python with:
$ pipenv --python path/to/python

也许我应该重新安装pipenv？

% which pipenv
/usr/local/bin/pipenv

% pip3 uninstall pipenv
Found existing installation: pipenv 2020.8.13
Uninstalling pipenv-2020.8.13:
  Would remove:
    /usr/local/bin/pipenv
    /usr/local/bin/pipenv-resolver
    /usr/local/lib/python3.8/site-packages/pipenv-2020.8.13.dist-info/*
    /usr/local/lib/python3.8/site-packages/pipenv/*
Proceed (y/n)? y
  Successfully uninstalled pipenv-2020.8.13

% pip3 install pipenv
Collecting pipenv
  Downloading pipenv-2020.11.15-py2.py3-none-any.whl (3.9 MB)
     |████████████████████████████████| 3.9 MB 2.9 MB/s 
Requirement already satisfied: pip>=18.0 in /usr/local/lib/python3.8/site-packages (from pipenv) (20.2.4)
Requirement already satisfied: virtualenv in /usr/local/lib/python3.8/site-packages (from pipenv) (20.0.31)
Requirement already satisfied: setuptools>=36.2.1 in /usr/local/lib/python3.8/site-packages (from pipenv) (50.3.2)
Requirement already satisfied: certifi in /usr/local/lib/python3.8/site-packages (from pipenv) (2020.6.20)
Requirement already satisfied: virtualenv-clone>=0.2.5 in /usr/local/lib/python3.8/site-packages (from pipenv) (0.5.4)
Requirement already satisfied: distlib<1,>=0.3.1 in /usr/local/lib/python3.8/site-packages (from virtualenv->pipenv) (0.3.1)
Requirement already satisfied: filelock<4,>=3.0.0 in /usr/local/lib/python3.8/site-packages (from virtualenv->pipenv) (3.0.12)
Collecting six<2,>=1.9.0
  Using cached six-1.15.0-py2.py3-none-any.whl (10 kB)
Requirement already satisfied: appdirs<2,>=1.4.3 in /usr/local/lib/python3.8/site-packages (from virtualenv->pipenv) (1.4.4)
Installing collected packages: pipenv, six
Successfully installed pipenv-2020.11.15 six-1.15.0

但仍然：

% pipenv install google-ads
Warning: Python 3.9 was not found on your system...
Neither 'pyenv' nor 'asdf' could be found to install Python.
You can specify specific versions of Python with:
$ pipenv --python path/to/python

实际上不行，但是让我们声明应该使用哪个 Python pipenv：

% pipenv --python /usr/local/opt/python@3.8/bin/python3 install google-ads
Creating a virtualenv for this project...
Pipfile: /Users/ralf/code/test_snippets/20-12-10_google_ads/Pipfile
Using /usr/local/opt/python@3.8/bin/python3 (3.8.6) to create virtualenv...
⠦ Creating virtual environment...created virtual environment CPython3.8.6.final.0-64 in 362ms
  creator CPython3Posix(dest=/Users/ralf/.local/share/virtualenvs/20-12-10_google_ads-S7vGVfKj, clear=False, global=False)
  seeder FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=/Users/ralf/Library/Application Support/virtualenv)
    added seed packages: pip==20.2.4, setuptools==50.3.2, wheel==0.35.1
  activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator

✔ Successfully created virtual environment! 
Virtualenv location: /Users/ralf/.local/share/virtualenvs/20-12-10_google_ads-S7vGVfKj
Warning: Your Pipfile requires python_version 3.9, but you are using 3.8.6 (/Users/ralf/.local/share/v/2/bin/python).
  $ pipenv --rm and rebuilding the virtual environment may resolve the issue.
  $ pipenv check will surely fail.
Warning: Your Pipfile requires python_version 3.9, but you are using 3.8.6 (/Users/ralf/.local/share/v/2/bin/python).
  $ pipenv --rm and rebuilding the virtual environment may resolve the issue.
  $ pipenv check will surely fail.
Installing google-ads...

pipenv --rm并且重建虚拟环境没有帮助。（我什至考虑简单地卸载 Python 3.9 并再次安装 Python 3.8 - 但不知道如何。）

有没有办法说服 pipenv 使用 Python 3.8？

标签： pythonhomebrewpipenv

解决方案

我很高兴您能够以自己的方式解决问题，但让我补充一些建议。一般来说，降级 Python（或实际上任何程序）通常不是受支持的操作。升级可能会升级与旧版本 Python 或其他依赖项不向后兼容的其他包中的依赖项。简而言之，你甚至不应该想要“降级”一个包，永远。

相反，您应该使用多个独立的环境，例如使用 virtualenv，这样，如果您出于某种原因需要较低版本，您可以用新的较低版本替换整个环境（请注意与“降级”的细微差别，因为您是完全使用新环境）。

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