原因：在安装python时，如果选择只为当前用户，以上问题就不会出现；如果选择所有用户，就会出现上述问题。

解决方法：

新建一个register.py 文件，把一下代码贴进去，保存。

## script to register Python 2.0 or later for use with win32all# and other extensions that require Python registry settings## written by Joakim Loew for Secret Labs AB / PythonWare## source:# http://www.pythonware.com/products/works/articles/regpy20.htm## modified by Valentine Gogichashvili as described in http://www.mail-archive.com/distutils-sig@python.org/msg10512.html import sys from _winreg import * # tweak as necessaryversion = sys.version[:3]installpath = sys.prefix regpath = "SOFTWARE\\Python\\Pythoncore\\%s\\" % (version)installkey = "InstallPath"pythonkey = "PythonPath"pythonpath = "%s;%s\\Lib\\;%s\\DLLs\\" % (    installpath, installpath, installpath) def RegisterPy():    try:        reg = OpenKey(HKEY_CURRENT_USER, regpath)    except EnvironmentError as e:        try:            reg = CreateKey(HKEY_CURRENT_USER, regpath)            SetValue(reg, installkey, REG_SZ, installpath)            SetValue(reg, pythonkey, REG_SZ, pythonpath)            CloseKey(reg)        except:            print "*** Unable to register!"            return        print "--- Python", version, "is now registered!"        return    if (QueryValue(reg, installkey) == installpath and        QueryValue(reg, pythonkey) == pythonpath):        CloseKey(reg)        print "=== Python", version, "is already registered!"        return    CloseKey(reg)    print "*** Unable to register!"    print "*** You probably have another Python installation!" if __name__ == "__main__":    RegisterPy()

输入以下命令：（要切换到register.py 目录下）

再次安装的时候，就能自动识别出来python2.7了。