Webapp2: Hello world

最近又在摸索 Google app engine，webapp2 基本上就是 GAE 內建的 web framework 啦，提供基本的 URL route、request handler、template、database 存取，相容於 WSGI 架構。

這是官方的 Hello world
helloworld.py

import webapp2

class MainPage(webapp2.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('Hello, webapp2 World!')

app = webapp2.WSGIApplication([
    ('/', MainPage)
], debug=True)

app.yaml

application: helloworld
version: 1
runtime: python27
api_version: 1
threadsafe: true

handlers:
- url: /.*
  script: helloworld.py

若使用 WSGI 來啓動 server，預設的 configuration file 就是 app.yaml，裡面會指明要執行哪個 python code，像上面就是 helloworld.py 這個檔案。執行後會去尋找"app"這個 object，所以物件的命名不能有錯，不然就會出現錯誤：

ERROR    2012-06-20 07:37:47,561 wsgi.py:189] 
Traceback (most recent call last):
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/runtime/wsgi.py", line 187, in Handle
    handler = _config_handle.add_wsgi_middleware(self._LoadHandler())
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/runtime/wsgi.py", line 239, in _LoadHandler
    raise ImportError('%s has no attribute %s' % (handler, name))
ImportError:  has no attribute app

如果不想透過 google app launcher 來啓動 project，請參考這一篇 Quick start (to use webapp2 outside of App Engine)，需要額外安裝三個 package。
程式碼如下，要自己另外帶起 http server：

import webapp2

class MainPage(webapp2.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('Hello, webapp2 World!')
app = webapp2.WSGIApplication([
    ('/', MainPage)
], debug=True)

def main():
    from paste import httpserver
    httpserver.serve(app, host='127.0.0.1', port='8080')

if __name__ == '__main__':
    main()

再從 command line 下達指令就可以了

$ python main.py
serving on http://127.0.0.1:8080