Spawning a GAE dev_appserver.py using gulp wrapper.

Gulpfile.js

const spawn = require( "child_process" ).spawn;

var server;

gulp.task( "gae", function() {
    if ( server ) server.kill();

    server = spawn( "python", [
        'C:/Users/<your user>/AppData/Local/Google/Cloud SDK/google-cloud-sdk/bin/dev_appserver.py',
        "--port", "8080",
        "<your out folder>"
    ], { stdio: "inherit" } );
} );

process.on( "exit", function() {
    if ( server ) server.kill();
} );

The path might be different for other people, but that is the default location (I believe).