I just had to install them. Then I used the free (and portable) soft at http://defaultprogramseditor.com/ under "File type settings"/"Context menu"/search:"py", chose .py file and added an 'open' command for the 2 IDLE by copying the existant command named 'open with IDLE, changing names to IDLE 3.4.1/2.7.8, and remplacing the files numbers of their respective versions in the program path. Now I have just to right click the .py file and chose which IDLE I want to use. Can do the same with direct interpreters if you prefer.

要在同一系统中安装和运行任何版本的Python，请遵循下面的指南。

例如，假设你想安装Python 2。3. Python。x在同一个Windows系统上。

Install both of their binary releases anywhere you want. When prompted do not register their file extensions and do not add them automatically to the PATH environment variable Running simply the command python the executable that is first met in PATH will be chosen for launch. In other words, add the Python directories manually. The one you add first will be selected when you type python. Consecutive python programs (increasing order that their directories are placed in PATH) will be chosen like so: py -2 for the second python py -3 for the third python etc.. No matter the order of "pythons" you can: run Python 2.x scripts using the command: py -2 (Python 3.x functionality) (ie. the first Python 2.x installation program found in your PATH will be selected) run Python 3.x scripts using the command: or py -3 (ie. the first Python 3.x installation program found in your PATH will be selected)

在我的例子中，我先安装了Python 2.7.14，然后安装了Python 3.5.3。这是我的PATH变量的开头:

路径=C:\文件程序\微软MPI\ \ \;C:\Python27;C:\文件程序\ python_3.6 \ scription \;C:\文件程序\ python_3.6 \

...

请注意，Python 2.7是第一个，Python 3.5是第二个。

因此，运行python命令将启动python 2.7(如果python 3.5，同样的命令将启动python 3.5)。 运行py -2将启动Python 2.7(因为恰好第二个Python是Python 3.5，与py -2不兼容)。 运行py -3会启动Python 3.5(因为它是Python 3.x) 如果你的路径中有另一个python，你会像这样启动:py -4。如果/当Python版本4发布时，这可能会改变。

现在py -4或py -5等在我的系统输出:请求的Python版本(4)未安装或请求的Python版本(5)未安装等。

希望这已经足够清楚了。

只有在Python IDE中运行代码才有效

我的windows操作系统上同时安装了Python 2.7和Python 3.3。如果我试图启动一个文件，它通常会在python 2.7 IDE上打开。我如何解决这个问题，是当我选择在python 3.3上运行我的代码时，我打开python 3.3 IDLE(python GUI)，选择文件，用IDLE打开我的文件并保存它。然后，当我运行我的代码时，它运行到我当前打开它的IDLE。反之亦然。

我按照这里的说明分三步做到了这一点:这都是从这里直接获取的:http://ipython.readthedocs.io/en/stable/install/kernel_install.html。我目前正在运行Python 2。已安装Anaconda 4.2.13。

1)首先安装最新版本的python:

conda create -n python3 python=3 ipykernel

2)下一步激活python3

activate python3

3)安装内核:

python -m ipykernel install --user

如果你已经安装了python3，想要安装python2，请切换上面的python2和python3。当你打开一个新的笔记本时，你现在可以在python2或python3之间进行选择。

You can install multiple versions of Python one machine, and during setup, you can choose to have one of them associate itself with Python file extensions. If you install modules, there will be different setup packages for different versions, or you can choose which version you want to target. Since they generally install themselves into the site-packages directory of the interpreter version, there shouldn't be any conflicts (but I haven't tested this). To choose which version of python, you would have to manually specify the path to the interpreter if it is not the default one. As far as I know, they would share the same PATH and PYTHONPATH variables, which may be a problem.

注:我使用的是Windows XP。我不知道其他版本是否会有这些变化，但我看不出有任何理由会发生变化。

我已经在windows 10pro上安装了python 2.7.13和python 3.6.1，当我尝试pip2或pip3时，我得到了相同的“致命错误”。

为了纠正这一点，我去python2和python3文件的python.exe的位置，并为每个文件创建一个副本，然后根据安装文件夹中的python版本将每个副本重命名为python2.exe和python3.exe。因此，我在每个python安装文件夹中都有一个python.exe文件和一个python2.exe或python3.exe，这取决于python版本。

当我输入pip2或pip3时，这解决了我的问题。