简单而近期

在windows上

1-假设您的系统中安装了不同版本的Python。使用以下命令进行检查:

> py --list
 -3.10-64 *
 -3.7-64

2-设置您首选的默认版本:

通过设置PY_PYTHON环境变量(例如PY_PYTHON=3.7)。 通过设置py.ini文件通常位于C:\Users\<您的用户名>\AppData\Local如果没有创建一个。例如，设置PY_PYTHON=3和PY_PYTHON3=3.7环境变量等价于INI文件包含:

[defaults]
python=3
python3=3.7

3-检查再次输入py——list:

> py --list
 -3.10-64 
 -3.7-64 *

4-如果你想用特定版本的python和pip运行虚拟环境，请参阅这篇文章。

Linux (Ubuntu)

在Linux上管理不同的python版本的一个简单方法是update-alternatives命令。这个命令使我们能够轻松地在同一软件的多个版本之间切换。

command format:update-alternatives --install link name path priority, the name is the generic name for the master link, the link is the name of its symlink, the path is the alternative being introduced for the master link, and priority is the priority of the alternatives group. Usage: Suppose you installed two versions of python (python3.10 , python3.7). Now by running this command you will link the command name (python3) to different versions of python and assign a priority number. A higher priority number means a higher priority.

$ update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.7 1
$ update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.10 2

使用此命令列出已安装的python版本:

$ update-alternatives --list python3
/usr/bin/python3.7
/usr/bin/python3.10

版本切换:执行以下命令后，只需手动选择所需python版本的优先级编号。

$ update-alternatives --config python3

There are 2 choices for the alternative python3 (providing /usr/bin/python3).

  Selection    Path                      Priority   Status
------------------------------------------------------------
  0            /usr/bin/python3.10   2         auto mode
* 1            /usr/bin/python3.7   1         manual mode
  2            /usr/bin/python3.10   2         manual mode

Press <enter> to keep the current choice[*], or type selection number: 2

显然，easy_install和pip有多个版本。看起来很乱。不管怎样，这是我在Ubuntu 12.10上安装Django for Python 2.7的方法:

$ sudo easy_install-2.7 pip
Searching for pip
Best match: pip 1.1
Adding pip 1.1 to easy-install.pth file
Installing pip-2.7 script to /usr/local/bin

Using /usr/lib/python2.7/dist-packages
Processing dependencies for pip
Finished processing dependencies for pip

$ sudo pip-2.7 install django
Downloading/unpacking django
  Downloading Django-1.5.1.tar.gz (8.0Mb): 8.0Mb downloaded
  Running setup.py egg_info for package django

    warning: no previously-included files matching '__pycache__' found under directory '*'
    warning: no previously-included files matching '*.py[co]' found under directory '*'
Installing collected packages: django
  Running setup.py install for django
    changing mode of build/scripts-2.7/django-admin.py from 644 to 755

    warning: no previously-included files matching '__pycache__' found under directory '*'
    warning: no previously-included files matching '*.py[co]' found under directory '*'
    changing mode of /usr/local/bin/django-admin.py to 755
Successfully installed django
Cleaning up...

$ python
Python 2.7.3 (default, Sep 26 2012, 21:51:14) 
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import django
>>> 

如果您有多个版本以及多个架构(32位，64位)，您将需要在版本的末尾添加-32或-64。

对于windows，进入cmd并输入py——list，它将生成您已安装的版本。列表如下所示:

Installed Pythons found by py Launcher for Windows
 -3.7-64 *
 -3.7-32
 -3.6-32

以完整命令为例:

py -3.6-32 -m pip install (package)

如果你想更深入地了解，在特定版本的python上安装特定版本的包，请在包后使用==(version)。举个例子，

py -3.6-32 -m pip install opencv-python==4.1.0.25

另一种可能的方法是使用conda和pip。有时你可能只想使用其中的一个，但如果你真的需要设置一个特定版本的python，我会将两者结合起来。

I create a starting conda enviroment with the python I want. As in here https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-environments.html. Alternatively you could set up the whole enviroment just using conda. conda create -n myenv python=3.6.4 Then activate your enviroment with the python you like. This command could change depending on the OS. source activae myenv Now you have your python active then you could continue using conda but if you need/want to use pip: python -m pip -r requirements.txt

这里有一种可能的方法。

要使用多个版本的pip，只需输入

Pip {version}和运行命令

示例:用于python 3.10

pip3.10 pip3.10列表

pip3.10

适用于Python 3.7

pip3.7 pip3.7列表

例如，如果您将其他版本(例如3.5)设置为默认版本，并希望为python 2.7安装PIP:

在https://pypi.python.org/pypi/pip (tar)下载PIP 解压缩tar文件 CD到文件的目录 Sudo python2.7 setup.py install