pyenv & virtualenv

pyenv，virtualenv，pyenv-virtualenv 简介。

What is the difference between venv, pyvenv, pyenv, virtualenv, virtualenvwrapper, pipenv, etc?

PEP 668 - externally-managed-environment#

pip - Upgraded Python; Do I have to reinstall all site-packages manually? - Stack Overflow

pip freeze > ~/Downloads/output/reqs.txt
pip3 freeze --path /usr/local/lib/python3.10/site-packages > ~/Downloads/pip-list.txt

pip3 install -r ~/Downloads/output/reqs.txt
pip3 install --user -r pip-list.txt

error: externally-managed-environment

× This environment is externally managed
╰─> To install Python packages system-wide, try brew install
    xyz, where xyz is the package you are trying to
    install.

    If you wish to install a Python library that isn't in Homebrew,
    use a virtual environment:

    python3 -m venv path/to/venv
    source path/to/venv/bin/activate
    python3 -m pip install xyz

    If you wish to install a Python application that isn't in Homebrew,
    it may be easiest to use 'pipx install xyz', which will manage a
    virtual environment for you. You can install pipx with

    brew install pipx

    You may restore the old behavior of pip by passing
    the '--break-system-packages' flag to pip, or by adding
    'break-system-packages = true' to your pip.conf file. The latter
    will permanently disable this error.

    If you disable this error, we STRONGLY recommend that you additionally
    pass the '--user' flag to pip, or set 'user = true' in your pip.conf
    file. Failure to do this can result in a broken Homebrew installation.

    Read more about this behavior here: <https://peps.python.org/pep-0668/>

note: If you believe this is a mistake, please contact your Python installation or OS distribution provider. You can override this, at the risk of breaking your Python installation or OS, by passing --break-system-packages.
hint: See PEP 668 for the detailed specification.

As the caveat suggests, we have two solutions to the problem.

use a virtual environment to install and upgrade pip packages, such as pipx
passing --break-system-packages to install and upgrade commands

venv#

venv — Creation of virtual environments

Source code: Lib/venv/, since Python 3.3

The venv module supports creating lightweight “virtual environments”, each with their own independent set of Python packages installed in their site directories. A virtual environment is created on top of an existing Python installation, known as the virtual environment's “base” Python, and may optionally be isolated from the packages in the base environment, so only those explicitly installed in the virtual environment are available.

When used from within a virtual environment, common installation tools such as pip will install Python packages into a virtual environment without needing to be told to do so explicitly.

A virtual environment is (amongst other things):

Used to contain a specific Python interpreter and software libraries and binaries which are needed to support a project (library or application). These are by default isolated from software in other virtual environments and Python interpreters and libraries installed in the operating system.
Contained in a directory, conventionally either named venv or .venv in the project directory, or under a container directory for lots of virtual environments, such as ~/.virtualenvs.
Not checked into source control systems such as Git.
Considered as disposable – it should be simple to delete and recreate it from scratch. You don't place any project code in the environment
Not considered as movable or copyable – you just recreate the same environment in the target location.

See PEP 405 for more background on Python virtual environments.

Availability: not Emscripten, not WASI.

pyenv#

github: pyenv / pyenv

Simple Python Version Management: pyenv

pyenv lets you easily switch between multiple versions of Python.
It's simple, unobtrusive, and follows the UNIX tradition of single-purpose tools that do one thing well.

intallation by Homebrew on macOS
Multiple Python installations on OS X
python 环境管理器pyenv 命令
 在 Mac OS X 10.10 安装 pyenv 的一个小坑
 CentOS 使用 pyenv, CentOS 6.4 下安装配置 pip 和 pyenv

pyenv 的美好之处在于它并没有使用将不同的 $PATH 植入不同的 shell 这种高耦合的工作方式，而是简单地在 $PATH 最前面插入了一个垫片路径（shims）：

~/.pyenv/shims:/usr/local/bin:/usr/bin:/bin

所有对 Python 可执行文件的查找都会首先被这个 shims 路径截获，从而架空了后面的系统路径。

Command Reference#

pyenv Command Reference

To list the all available versions of Python, including Anaconda, Jython, pypy, and stackless use:

列出所有可安装的 python 版本：

faner@MBP-FAN:~|⇒  pyenv install --list
Available versions:
  2.1.3
  2.2.3

Then install the desired versions:

安装特定的 python 版本：

$ pyenv install 2.7.6
$ pyenv install 2.6.8

Lists all Python versions known to pyenv, and shows an asterisk next to the currently active version.

列出已经安装的 python 版本：

faner@MBP-FAN:~|⇒  pyenv versions
* system (set by /Users/faner/.pyenv/version)

查看当前正在使用的 python 版本：

faner@MBP-FAN:~|⇒  pyenv version
system (set by /Users/faner/.pyenv/version)

Uninstall a specific Python version.

卸载指定版本的 python：

Usage: pyenv uninstall [-f|--force] <version>

   -f  Attempt to remove the specified version without prompting
       for confirmation. If the version does not exist, do not
       display an error message.

Displays the full path to the executable that pyenv will invoke when you run the given command.

列出指定版本 python 的实际路径：

$ pyenv which python3.3
/home/yyuu/.pyenv/versions/3.3.3/bin/python3.3

virtualenv#

virtualenv is a tool to create isolated Python environments.

Docs » Virtualenv

ubuntu 使用 pyenv 和 virtualenv 搭建多版本虚拟开发环境
 CentOS 6.8 使用 pyenv + virtualenv 打造多版本 Python 开发环境