This article describes in detail for everyone under Win10 python3.5 and python2.7 environment variable configuration tutorial, installation procedures described in this paper is very detailed, with some reference value, small partners who are interested can refer to
this paper introduced the python2 python3 detailed method and installation for everyone to share.
A, Windows systems
Many children's shoes before asking tutorial does not describe how to install python3.5, now supplemented update it.
(A) mounting python3.5
1, download
into the Python official website www.python.org, in the "Downloads" drop-down menu, click on the right half python3.5.2 version to download, it will automatically download the 32-bit.
If you need 64-bit, click on the left half of the "Windows", select the second item "Latest Python 3 Release - Python 3.5.2 ". 
In the "Files" in the countdown to select the fifth "Windows x86-64 executable installer" download. 
2, installation
Installation has just been downloaded from the installation package, the installation process shown in FIG., The default configuration, select the "Install Now", the following check Add Python3.5 to PATH. 
(B) mounting python2.7
1. Download
进入Python官网www.python.org，在“Downloads”下拉菜单中的右半部分直接点击即可下载，从兼容方面考虑建议下载Python 2.7版本。
如果想要下载64位的，点击左半部分“Windows”，选择第一项“Latest Python 2 Release - Python 2.7.11”，
在“Files”里选择倒数第二个“Windows x86-64 MSI installer”下载。
2、安装
安装刚才已经下载下来的安装包， 安装过程下图所示，一路默认操作。
3、配置
右击桌面上的“此电脑”—>“属性”—>“高级系统设置”—>右下角“环境变量”—>双击“系统变量”里的“Path”—>点击“新建”—>输入刚才的安装位置“C:\Python27;”，得到新建后的结果，然后一步步确定回去。
win+R，cmd调出命令行，输入命令“python”，就可以有相关显示。
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二、Ubuntu系统
如果计算机的操作系统是Linux的某个发行版，比如Ubuntu 等，我这里是用elementary OS亲测的，其实都大同小异，因为它们都已经安装好了Python的编程环境，只需要打开终端Shell，输入python，回车之后就会出现跟上文windows中类似的结果。
Without the programming environment, it is necessary to install the easiest method is to input terminal
sudo apt-get install python
How to upgrade to version 2.7 comes with the initial 3.5 do the following steps:
sudo apt-get install python3.5
As the default is Python2, it is understood, is not compatible with versions 2 and 3, but the underlying and using 2, it can not unload 2, just to the default Python 3 can point to.
sudo rm /usr/bin/python
sudo ln -s /usr/bin/python3.5 /usr/bin/python
[Extended]
python is now mainly used in two versions: 2.x and 3.x, but these two versions of the grammar there are many different, python3.x not backward compatible with the 2.x. Although python 3.x is the future mainstream, but many tools and personally prefer python2.x, it is sometimes possible to simultaneously use both versions, then install two python versions on the same computer is very necessary a.
Python3 coexistence and resolve python2
