Having installed python 2.7, and added python directory to PATH variable. I started windows command line and typed "python" + enter. It neither reports error nor switch to python command line. Instead just pop up python version info and revert to windows command prompt as below
Microsoft Windows [Version 10.0.14393]
(c) 2016 Microsoft Corporation. All rights reserved.
C:\Users\User>python
Python 2.7.13 (v2.7.13:a06454b1afa1, Dec 17 2016, 20:53:40) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
C:\Users\User>
Restart computer does not help either. Just cannot find a similar case so post here.