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Python 环境变量

下面几个重要的环境变量，它应用于Python：

变量名描述PYTHONPATHPYTHONPATH是Python搜索路径，默认我们import的模块都会从PYTHONPATH里面寻找。PYTHONSTARTUPPython启动后，先寻找PYTHONSTARTUP环境变量，然后执行此变量指定的文件中的代码。PYTHONCASEOK加入PYTHONCASEOK的环境变量, 就会使python导入模块的时候不区分大小写.PYTHONHOME另一种模块搜索路径。它通常内嵌于的PYTHONSTARTUP或PYTHONPATH目录中，使得两个模块库更容易切换。

通常我们会在命令行上设置PYTHONPATH。在执行脚本之前先执行设置PYTHONPATH的命令。

例如windows上，设置PYTHONPATH的命令为：

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1. SET ROOT_DIR=%~dp0  
2. SET PYTHONPATH=%PYTHONPATH%;%ROOT_DIR%src\main\python;%ROOT_DIR%src\test\python;%ROOT_DIR%generated\pyxb;%ROOT_DIR%  

这样就将我们在当前目录下的src\main\python，src\test\python，generated\pyxb三个文件夹放到pythonpath里面了，我们就可以直接导入这三个文件夹里面的模块了。

You know what has worked for me really well on windows.

My Computer > Properties > Advanced System Settings > Environment Variables >

Then under system variables I create a new Variable called PythonPath. In this variable I have C:\Python27\Lib;C:\Python27\DLLs;C:\Python27\Lib\lib-tk;C:\other-folders-on-the-path

This is the best way that has worked for me which I hadn't found in any of the docs offered.

EDIT: For those who are not able to get it, Please add

C:\Python27;

along with it. Else it will never work.

今天在调试Evernote SDK时， 遇到PythonPath的问题。 查了很多资料，有说用系统环境变量添加PythonPath， 有说在注册表中的PythonPath添加新Default字段， 但是对于我来说都没有效果， 很奇怪。 
最后还是在代码里显式添加sys.path才好用：

import sys
import hashlib
import binascii
import time

if "..\\lib" not in sys.path:
     sys.path.append(r"..\\lib")

Windows 7 Professional I Modified @mongoose_za's answer to make it easier to change the python version:

1. [Right Click]Computer > Properties >Advanced System Settings > Environment Variables
2. Click [New] under "System Variable"
3. Variable Name: PY_HOME, Variable Value:C:\path\to\python\version 
4. Click [OK]
5. Locate the "Path" System variable and click [Edit]

6. Add the following to the existing variable:

   %PY_HOME%;%PY_HOME%\Lib;%PY_HOME%\DLLs;%PY_HOME%\Lib\lib-tk; 

7. Click [OK] to close all of the windows.

As a final sanity check open a command prompt and enter python. You should see

>python [whatever version you are using]

If you need to switch between versions, you only need to modify the PY_HOME variable to point to the proper directory. This is bit easier to manage if you need multiple python versions installed.