用npm安装Node-Sass老是报错是怎么回事？

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错误代码：gypERR!configureerrorgypERR!stackError:Can'tfindPythonexecutable"python",youcansetthePYTHONenvvariable.gypERR!stackatPythonFinder.failNoPython(C:Users***AppDataRoamingnpmnode_modulesnode-sassnode_modulesnode-gyplibconfigure.js:483:19)gypERR!stackatPythonFinder.(C:Users***AppDataRoamingnpmnode_modulesnode-sassnode_modulesnode-gyplibconfigure.js:508:16)gypERR!stackatC:Users***AppDataRoamingnpmnode_modulesnode-sassnode_modulesgraceful-fspolyfills.js:284:29gypERR!stackatFSReqWrap.oncomplete(fs.js:152:21)gypERR!SystemWindows_NT6.1.7601gypERR!command"D:\ProgramFiles\nodejs\node.exe""C:\Users\*\AppData\Roaming\npm\node_modules\node-sass\node_modules\node-gyp\bin\node-gyp.js""rebuild""--verbose""--libsass_ext=""--libsass_cflags=""--libsass_ldflags=""--libsass_library="gypERR!cwdC:Users***AppDataRoamingnpmnode_modulesnode-sassgypERR!node-vv8.0.0gypERR!node-gyp-vv3.6.2gypERR!notokBuildfailedwitherrorcode:1npmERR!codeELIFECYCLEnpmERR!errno1npmERR!node-sass@4.5.3postinstall:nodescripts/build.jsnpmERR!Exitstatus1npmERR!npmERR![e-mail]!Thisisprobablynotaproblemwithnpm.Thereislikelyadditionalloggingoutputabove.npmERR!Acompletelogofthisruncanbefoundin:npmERR!C:Users***AppDataRoamingnpm-cache_logs2017-07-06T01_07_47_983Z-debug.log求大佬指点，给大佬递茶。公司内网，代理已经配置好，不过我的权限可能有的网站和端口会访问不了，github能上，node.js官网能上，源用的是cnpm。