google app engine application architecture in python

Question

I am pretty new to google app engine and python. After successfully uploading an application, I am stuck with a basic question.

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

This is the code block which is generally used to map the request with the class that handles it. However there is a section in app.yaml which allows specifying handler for individual url.

My question is what is the correct architecture of a python application on google app engine. What if my application has several hundreds of classes for handling different request ?, do I have to specify all of them here in this code ?

I have googled but could not find a satisfactory answer. Link to a good tutorial or documentation would be a great help.

Wingo · Accepted Answer · 2013-02-16 12:24:36Z

2

Basically, you define the app to be used in app.yaml. For example, if you've got multiple apps, you can specify here which to use.

Yes, you have to specify all the allowed URLs here (in main.py). Otherwise the request will get 404. However, you can use regular expressions to make certain type of addresses to match the given handler.

Check out the tutorial: https://developers.google.com/appengine/docs/python/gettingstartedpython27/usingwebapp

Documentation for URI routing: http://webapp-improved.appspot.com/guide/routing.html?highlight=url

answered Feb 16, 2013 at 12:24

Wingo

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Nijin Narayanan · Accepted Answer · 2013-02-16 12:13:51Z

1

You can do like this.

In app.yaml

- url: /service/.*
  script: service.app

- url: .*
  script: main.app

In service.py

url_map = [
    ('.*/user.*', 'service.UserHandler'),   
    ('.*/data/show/', 'appname.service.DataShowHandler'),
    ('.*/data.*', 'appname.service.DataHandler'),
]

app = webapp2.WSGIApplication(url_map)

When you tried to access http://your-appid.com/service/user, appengine will excecute GET function of UserHandler Class in service.py which is located in the Root Folder.

When you tried to access http://your-appid.com/service/data/show, appengine will excecute GET function of DataShowHandler Class in service.py which is located in the Root/appname Folder.

answered Feb 16, 2013 at 12:13

Nijin Narayanan

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1 Comment

Murtuza Kabul Over a year ago

Your answer helped me in understanding the behavior of python app. It was very helpful

voscausa · Accepted Answer · 2013-02-16 12:26:04Z

1

I have two anwers :

1) You can use webapp2 routing to handle the requests and uri routing. This is very powerfull. You can use url templates and / or write your own custom dispatcher.

2) For a lot of requests you can use a single URL and use a session / state to find out how to continue after a post. This means : you do not have to use a request handler for every request.

answered Feb 16, 2013 at 12:26

voscausa

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Comments

Remco Haszing · Accepted Answer · 2013-02-16 12:01:47Z

0

app.yaml can be used for setting such as secure and login options, though I personally don't use them.
I use main.py to map all urls to the right handlers.

answered Feb 16, 2013 at 12:01

Remco Haszing

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