Google app-engine-with-python
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This document summarizes a presentation on developing applications for Google App Engine using Python. It introduces App Engine as a platform for hosting scalable web applications without having to manage infrastructure. Key aspects covered include setting up the development environment, defining application configuration and handlers, using frameworks like WSGI and Webapp2, rendering templates, accessing the Datastore NoSQL database, and deploying applications to App Engine. Common questions about App Engine capabilities and limitations are also addressed.
![Set up Your Env
✔ Install Python :-)
✔
Download App Engine SDK →
➔ a web server application that simulates the App Engine env
➔ dev_appserver.py myapp → for a local webserver
➔ appcfg.py update myapp → to deploy to the cloud
✔ Install Eclipse [ Optional ]
✔ Install Pydev and App Engine Eclipse Plugin [ Optional ]
https://developers.google.com/appengine/downloads](https://image.slidesharecdn.com/google-app-engine-with-python-120618085042-phpapp02/85/Google-app-engine-with-python-6-320.jpg)
![Webapp2 framework
● A webapp2 application has 2 parts:
➔ one or more RequestHandler classes that process requests
and build responses
➔ a WSGIApplication instance that routes incoming requests to
handlers based on the URL
import webapp2
class MainPage(webapp2.RequestHandler):
def get(self):
self.response.headers['Content-Type'] = 'text/plain'
self.response.out.write('Hello, webapp World!')
app = webapp2.WSGIApplication([('/', MainPage)],
debug=True)](https://image.slidesharecdn.com/google-app-engine-with-python-120618085042-phpapp02/85/Google-app-engine-with-python-9-320.jpg)
![Templates
libraries:
● Import jinja2 in app.yaml - name: jinja2
version: latest
● Point jinja2 to your template dir
jinjadir = jinja2.Environment(loader=jinja2.FileSystemLoader(template_dir))
● Load your templates
fom = jinjadir.get_template('form.template')
● Render your templates
fom.render({'items':['a', 'b', 'c']})](https://image.slidesharecdn.com/google-app-engine-with-python-120618085042-phpapp02/85/Google-app-engine-with-python-10-320.jpg)
Google app-engine-with-python
- 1. BangPypers June Meetup 2012 Google App Engine with Python Deepak Garg Citrix R&D, Bengaluru [email protected] Google App Engine with Python by Deepak Garg is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License. Based on a work at www.slideshare.net/khinnu4u/presentations.
- 2. Contents ✔ What my App needs ? ✔ App Engine ? ✔ Python for App Engine ✔ Set Up Your Env ✔ app.yaml ✔ Wsgi ✔ Webapp2 framework ✔ Templates ✔ Static Files ✔ DataStore ✔ Admin & DashBoard ✔ App Engine Feature Set ✔ FAQ
- 3. What my App needs ? ● App = Business Logic + IT ● IT => deploying and maintaining web and db, server backup, HA, scale out/in, LB etc. etc.. Upgrades, licenses Monitoring ● IT efforts remain consistent and similar across different apps, Business Logic differs ● Developers want to focus on the business logic
- 4. App Engine ? ✔ Google App Engine (aka GAE) is a Platform as a Service (PaaS) cloud computing platform for developing and hosting web applications in Google-managed data centers ✔ Applications are sandboxed and run in Google’s best-of-breed data centers around the world ✔ App Engine offers automatic scaling for web applications—as the number of requests increases for an application ✔ App Engine automatically allocates more resources for the web application to handle the additional demand ✔ GAE is free up to a certain level of consumed resources ✔ Fees are charged for additional storage, bandwidth, or instance hours
- 5. Python for App Engine ● Python → 2.5, 2.7 ● Frameworks → Django, web2py, webapp, cherryPy, pylons ● External Libraries → jinja2, lxml, numpy, webob, yaml, pil, pycrypto, setuptools etc..
- 6. Set up Your Env ✔ Install Python :-) ✔ Download App Engine SDK → ➔ a web server application that simulates the App Engine env ➔ dev_appserver.py myapp → for a local webserver ➔ appcfg.py update myapp → to deploy to the cloud ✔ Install Eclipse [ Optional ] ✔ Install Pydev and App Engine Eclipse Plugin [ Optional ] https://developers.google.com/appengine/downloads
- 7. app.yaml ● specifies runtime configuration → versions, url handlers etc. application identifier is application: helloworld ”helloworld”, name used to version: 1 register your application runtime: python27 with App Engine api_version: 1 Uploading application with threadsafe: true diff version no. creates different versions on the handlers: server - url: /.* code runs in the python27 script: helloworld.app runtime environment, version "1" app is threadsafe or not URL Routers → urls matching the regex are captured
- 8. WSGI A WSGI application is a callable with the following signature: def application(environ, start_response) environ is a dictionary which contains everything in os.environ plus variables which contain data about the HTTP reqeust. start_response is a callable which the application calls to set the status code and headers for a response, before returning the body of the response. start_response(status, response_headers, exc_info=None) The return value for the WSGI application is an iterable object. Each item in the iterable is a chunk of the HTTP response body as a byte string.
- 9. Webapp2 framework ● A webapp2 application has 2 parts: ➔ one or more RequestHandler classes that process requests and build responses ➔ a WSGIApplication instance that routes incoming requests to handlers based on the URL import webapp2 class MainPage(webapp2.RequestHandler): def get(self): self.response.headers['Content-Type'] = 'text/plain' self.response.out.write('Hello, webapp World!') app = webapp2.WSGIApplication([('/', MainPage)], debug=True)
- 10. Templates libraries: ● Import jinja2 in app.yaml - name: jinja2 version: latest ● Point jinja2 to your template dir jinjadir = jinja2.Environment(loader=jinja2.FileSystemLoader(template_dir)) ● Load your templates fom = jinjadir.get_template('form.template') ● Render your templates fom.render({'items':['a', 'b', 'c']})
- 11. Static Files ● create your static directory url: /mystatic ● point to it in app.yaml static_dir: mystatic Deploy ● register your app_id https://appengine.google.com/ ● point to it in app.yaml application: app_id version: 1 ● update version no. ● upload your app appcfg.py update myapp ● browse your app :) http://app_id.appspot.com/
- 12. DataStore ● Google’s Bigtable high-performance distributed database ● Not a Relational DB – scales awesomely well ! ● Replicate data across multiple DCs ● Data is written to the Datastore in objects known as entities. Each entity has a key that uniquely identifies it ● Every entity has a unique identifier ● An entity can optionally designate another entity as its parent and thus form a hierarchy Object Oriented Relational DB DataStore Class Table Kind Object Record Entity Attribute Column Propery https://developers.google.com/appengine/docs/python/datastore/entities
- 13. DataStore ● define your entity class from google.appengine.ext import db ● create object (entity) class PyperDB(db.Model): name = db.StringProperty(multiline=True); ● put it in db status = db.BooleanProperty(); user_id = db.UserProperty(); ● check it in DB viewer time = db.DateTimeProperty(auto_now_add=True) us = PyperDB(name=val, status=False, user_id=uid) us.put(); ● Model defines a unique id by key = us.key().id_or_name() default for each entity result = db.GqlQuery("SELECT * " ● Fetch data using GQL queries "FROM PyperDB " ”WHERE ANCESTOR IS :1 " ”ORDER BY date DESC LIMIT 10",key_value) ● Delete uis = PyperDB.all() for p in uis: p.delete() https://developers.google.com/appengine/docs/python/datastore/gqlreference
- 14. Admin & DashBoard ● Local Admin console running at http://localhost:9999/_ah/admin ● GAE Dashboard, logs, DS viewer etc. are used to manage your app
- 15. GAE Features https://developers.google.com/appengine/docs/python/apis
- 16. FAQ ● Can I run existing django apps on App Engine ? ● Can I move my App Engine application to my hosting environment ? Yes, Look at django-rel (django for non-relational db http://www.allbuttonspressed.com/projects/django-nonrel http://www.allbuttonspressed.com/projects/djangoappengine ● Can I run any Python code on App Engine ? With certain limitations → cannot write to FS but you can read ( from flat file you uploaded ) cannot open a socket, can't make system call, can't respond slowly to requests ( 60 secs )
- 17. Many Thanks ! [email protected] @donji github.com/gargdeepak