|
|
| Line 26: |
Line 26: |
|
| |
|
| AngularJS creates single page web applications which makes [http://en.wikipedia.org/wiki/Search_engine_optimization Search Engine Optimization] extremely tricky, i.e., users won't be able to search on the website efficiently. Also, it is designed to run on the client side which means that for any real application a back end will be required. Thus, Rails came into picture. It provides a back end to the application so that large amount of data can be stored and also the web pages are rendered by Rails on the server, which makes them available to be searched by Google. | | AngularJS creates single page web applications which makes [http://en.wikipedia.org/wiki/Search_engine_optimization Search Engine Optimization] extremely tricky, i.e., users won't be able to search on the website efficiently. Also, it is designed to run on the client side which means that for any real application a back end will be required. Thus, Rails came into picture. It provides a back end to the application so that large amount of data can be stored and also the web pages are rendered by Rails on the server, which makes them available to be searched by Google. |
|
| |
| ==Installation==
| |
|
| |
| ===Requirements===
| |
| CherryPy requires a Python version between 2.3 and 3.4 inclusively. Certain features require packages but none are mandatory for installation.<ref>http://docs.cherrypy.org/en/latest/install.html</ref>
| |
| *[http://routes.readthedocs.org/en/latest/ routes] for declarative URL mapping dispatcher
| |
| *[http://pythonhosted.org//psycopg2/ psycopg2] for [http://en.wikipedia.org/wiki/PostgreSQL PostgreSQL] database backend session
| |
| *[http://sourceforge.net/projects/pywin32/ pywin32] for Windows services
| |
| *[https://github.com/linsomniac/python-memcached python-memcached] for [http://en.wikipedia.org/wiki/Memcached Memcached] backend session
| |
| *[https://github.com/simplejson/simplejson simplejson] for a better [http://en.wikipedia.org/wiki/JSON JSON] support
| |
| *[https://github.com/pyca/pyopenssl pyOpenSSL] if your Python environment does not have the built in [http://en.wikipedia.org/wiki/Transport_Layer_Security ssl] module
| |
|
| |
|
| |
| ===Installing===
| |
| CherryPy can be installed through common Python package managers with the following commands:<ref>http://docs.cherrypy.org/en/latest/install.html</ref><br/>
| |
|
| |
| Install (choose on of the following commands appropriately):
| |
| $ easy_install cherrypy
| |
| $ pip install cherrypy
| |
| $ yum install python-cherrypy
| |
| $ apt-get install python python-dev
| |
|
| |
| ===Install via yum===
| |
| CherryPy is provided by the fedora base repository. In [http://en.wikipedia.org/wiki/Fedora_%28operating_system%29 Fedora] (and other [http://en.wikipedia.org/wiki/RPM_Package_Manager RPM] based Linux distributions, such as [http://en.wikipedia.org/wiki/CentOS CentOS] and [http://en.wikipedia.org/wiki/Red_Hat_Enterprise_Linux Red Hat Enterprise Linux]):<br/>
| |
| $ yum install python-cherrypy
| |
|
| |
| ===Install via apt-get===
| |
| CherryPy is also provided in the [http://en.wikipedia.org/wiki/Ubuntu_(operating_system) Ubuntu] base repository. In Ubuntu (and other [http://en.wikipedia.org/wiki/Debian Debian]-based Linux distributions such as Debian and [http://en.wikipedia.org/wiki/Linux_Mint Linux Mint]):
| |
| $ apt-get install python python-dev
| |
|
| |
| ===Installation from source===
| |
| The source code is hosted on [http://en.wikipedia.org/wiki/Bitbucket BitBucket] and requires [http://en.wikipedia.org/wiki/Mercurial Mercurial] to pull and install from the site itself.
| |
| $ hg clone https://bitbucket.org/cherrypy/cherrypy
| |
| $ cd cherrypy
| |
| $ python setup.py install
| |
|
| |
| Alternatively, the source can be manually downloaded from [https://bitbucket.org/cherrypy/cherrypy/downloads here] in a tarball.
| |
| $ tar -xvf CherryPy-#.#.#.tar.gz
| |
| $ cd CherryPy-#.#.#
| |
| $ python setup.py install
| |
|
| |
| ===Install for Windows===
| |
| *If you are using Windows, install Linux and follow any of the a forementioned methods.
| |
| *If you absolutely must use windows, you can download the .exe file to install CherryPy from [https://bitbucket.org/cherrypy/cherrypy/downloads here].
| |
|
| |
| ==Interface==
| |
|
| |
| CherryPy is meant to be pythonic, meaning that development time is meant to be minimized and code is meant to be sparse and clean <ref>http://docs.cherrypy.org/en/latest/intro.html</ref>
| |
|
| |
| ===Basic Example===
| |
| Lets look at a hello world example<ref>https://cherrypy.readthedocs.org/en/3.2.6/concepts/basics.html</ref><ref>http://stackoverflow.com/questions/419163/what-does-if-name-main-do</ref>
| |
| <pre>
| |
| #Use the cherrypy python library
| |
| import cherrypy
| |
|
| |
| #Hello World project
| |
| class HelloWorld(object):
| |
|
| |
| # index page
| |
| def index(self):
| |
| # Return the page contents
| |
| return “Hello World!”
| |
|
| |
| # Allow the page to be visible
| |
| index.exposed = True
| |
|
| |
| #designates this module as main
| |
| if __name__ == ‘__main__’:
| |
|
| |
| # instantiates app and starts server
| |
| cherrypy.quickstart(HelloWorld())
| |
|
| |
| </pre>
| |
| The above script sets up a basic Hello World application, by defining the index page (http://localhost:8080/) as an object that returns the string “Hello World!”. The page is exposed, meaning that the method can be called to answer a [http://en.wikipedia.org/wiki/Representational_state_transfer RESTful] request. Otherwise, the method is internal only. This is similar to making a method public in Java. <ref>http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html</ref>
| |
|
| |
| ===Routing, Parameters, and Exposure===
| |
| Routing is the act of finding the appropriate code to handle a request. CherryPy uses a dispatcher to perform most of these, but premade dispatchers exist to handle more sophisticated handling of request. The most common is a page handler (the name of the object). Parameters can be passed into the handler via http query strings. These strings are appended to the URL of a site after a "?". Exposure is just the way CherryPy prevents access to objects from the users. Without the exposed attribute set to true, an object won't be accessible to the user.
| |
| <pre>
| |
| #import python library
| |
| import cherrypy
| |
|
| |
| #More Routes application
| |
| class MoreRoutes(object):
| |
|
| |
| # Method decorator for index and equates to index.exposed = True
| |
| @cherrypy.expose
| |
| def index(self):
| |
| return "Hello world!"
| |
|
| |
| # http://localhost:8080/route1
| |
| def route1(self, id=”charles”):
| |
| # http://localhost:8080/route1?id=somestring
| |
| return “Your name is ” + id
| |
|
| |
| # Params passed as a GET request.
| |
| # Default string is “charles”
| |
| route1.exposed = True
| |
|
| |
| # No explicit indication of exposure so calling this route will generate a 404 error
| |
| def route2(self):
| |
| return “Still another one”
| |
|
| |
| if __name__ == '__main__':
| |
| cherrypy.quickstart(MoreRoutes())
| |
|
| |
| </pre>
| |
|
| |
| The above shows how multiple routes are handled from the Hello World application and the expose decorator. Since route2 is not exposed, the user can not access it and will be shown a 404 HTTP status code (Not Found error).
| |
|
| |
| ===Multiple Applications===
| |
|
| |
|
| |
| <pre>
| |
| import cherrypy
| |
| #blog module
| |
| class Blog(object):
| |
| ...<blog code>...
| |
| #forum module
| |
| class Forum(object):
| |
| ...<forum code>...
| |
| #”main” method
| |
| if __name__ == '__main__':
| |
| #designates the blog to be under /blog route
| |
| cherrypy.tree.mount(Blog(), ‘/blog’, “blog.conf”)
| |
| #designates the forum to be under /forum route
| |
| cherrypy.tree.mount(Forum(), ‘/forum’, “forum.conf”)
| |
| </pre> <ref>http://docs.cherrypy.org/en/latest/basics.html#multiple-applications</ref>
| |
| In the above example, the blog would be found under /blog in the URL, wheras the forum will be mounted at /forum in the application tree. The XXX.conf files are configuration files, which are dictionaries containing string keys and polymorphic values and can be used to set attributes on the engine, server, request, response, and log objects. <ref>https://cherrypy.readthedocs.org/en/3.2.6/concepts/config.html</ref>
| |
|
| |
| ===Database Support===
| |
| CherryPy offers multiple database integration possibilities including
| |
| *[http://en.wikipedia.org/wiki/Relational_database Relational]: [http://en.wikipedia.org/wiki/PostgreSQL PostgreSQL], [http://en.wikipedia.org/wiki/SQLite SQLite], [http://en.wikipedia.org/wiki/MariaDB MariaDB], [http://en.wikipedia.org/wiki/Firebird_%28database_server%29 Firebird]
| |
| *[http://en.wikipedia.org/wiki/Column-oriented_DBMS Column-Oriented]: [http://en.wikipedia.org/wiki/Apache_HBase HBase], [http://en.wikipedia.org/wiki/Apache_Cassandra Cassandra]
| |
| *[http://en.wikipedia.org/wiki/NoSQL#Key.E2.80.93value_stores Key-Store]: [http://en.wikipedia.org/wiki/Redis Redis], [http://en.wikipedia.org/wiki/Memcached Memcached]
| |
| *[http://en.wikipedia.org/wiki/Document-oriented_database Document-Oriented]: [http://en.wikipedia.org/wiki/CouchDB Couchdb], [http://en.wikipedia.org/wiki/MongoDB MongoDB]
| |
| *[http://en.wikipedia.org/wiki/Graph_database Graph-Oriented]: [http://en.wikipedia.org/wiki/Neo4j Neo4j]<br/>
| |
| Unfortunately, unlike [https://en.wikipedia.org/wiki/Ruby_on_Rails Ruby on Rails], CherryPy does not have a sophisticated [https://en.wikipedia.org/wiki/Active_record_pattern#Ruby Active Record Pattern] based class for database abstraction, and the database connection has to be established manually. The queries are constructed as static [https://en.wikipedia.org/wiki/SQL SQL] strings with values concatenated during function calls.<br/>
| |
|
| |
| Here is an example of how it would look like<ref>http://cherrypy.readthedocs.org/en/latest/tutorials.html#tutorial-9-data-is-all-my-life</ref>
| |
| <pre>
| |
|
| |
| # import the Handles
| |
| import MySQLdb
| |
| import cherrypy
| |
|
| |
| # defining the connection function
| |
| def connect(thread_index):
| |
| # Create a connection and store it in the current thread
| |
| cherrypy.thread_data.db = MySQLdb.connect('host', 'user', 'password', 'dbname')
| |
|
| |
| # tell cherrypy to call connect function for each thread
| |
| cherrypy.engine.subscribe('start_thread', connect)
| |
|
| |
| # example query function
| |
| @cherrypy.expose
| |
| def count(val)
| |
| # fetching instance of db connection
| |
| c = cherrypy.thread_data.db.cursor()
| |
| # executing query
| |
| c.execute( 'select count(‘ + val + ’) from table' )
| |
| # fetching results from db
| |
| res = c.fetchone()
| |
| # releasing instance of the connection
| |
| c.close()
| |
| # returning the count value
| |
| return res
| |
|
| |
| </pre>
| |
|
| |
| ==RESTful CherryPy==
| |
| [http://en.wikipedia.org/wiki/Representational_state_transfer REST] (Representational State Transfer) is an abstraction of the architectural elements within a distributed hypermedia system. It ignores the details of component implementation and protocol syntax in order to focus on the roles of components, the constraints upon their interaction with other components, and their interpretation of significant data elements. It encompasses the fundamental constraints upon components, connectors, and data that define the basis of the Web architecture, and thus the essence of its behavior as a network-based application. <ref>http://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm</ref><br/>
| |
| In othe words, REST is defined by four interface constraints: identification of resources, manipulation of resources through representations, self-descriptive messages, and hypermedia as the engine of application state.<ref>https://cherrypy.readthedocs.org/en/3.2.6/progguide/REST.html</ref>
| |
|
| |
| ===Identification of Resources===
| |
| Since Cherrypy is an HTTP service provider, resources are referenced by HTTP URIs (Uniform Resource Identifiers), which consist of a scheme, hierarchical identitfier, query, and fragment.<ref>https://cherrypy.readthedocs.org/en/3.3.0/progguide/REST.html#implementing-rest-in-cherrypy</ref><br/>
| |
| *Scheme: in [http://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol http], the scheme is always http or [http://en.wikipedia.org/wiki/HTTP_Secure https].
| |
| *Hierarchical Identifier: consists of an authority and a path (host/port and a path similar to the system file path but not the actual path). The path is mapped to Python Objects via a dispatch mechanism.
| |
|
| |
| ===Manipulation of Resources Through Representations===
| |
| The standard [http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html HTTP methods] are as follows<ref>https://cherrypy.readthedocs.org/en/3.3.0/progguide/REST.html#manipulation-of-resources-through-representations</ref>
| |
| *<code>GET</code> retrieves the state of a specific resource
| |
| *<code>PUT</code> creates or replaces the state of a specific resource
| |
| *<code>POST</code> passes information to a resource to use as it sees fit
| |
| *<code>DELETE</code> removes resources
| |
|
| |
| ===Self-Descriptive Messages===
| |
| REST requires messages to be self-descriptive, meaning everything about a message is within the message itself. Such information can be found in the method headers or the definitions of the message’s media type. cherrypy.request.headers and cherrypy.response.headers are used to get this information. Custom-Types are allowed as well.<ref>https://cherrypy.readthedocs.org/en/3.3.0/progguide/REST.html#self-descriptive-messages</ref>
| |
|
| |
| ===Hypermedia as the Engine of the Application State===
| |
| Since REST is stateless and the state is maintained by the application in question, sessions are not maintained by REST, so, by association, CherryPy does not enable sessions by default. However, the REST server helps clients maintain a meaningful state through meaningful URIs<ref>https://cherrypy.readthedocs.org/en/3.3.0/progguide/REST.html#hypermedia-as-the-engine-of-application-state</ref>
| |
|
| |
| ==Crash Course==
| |
|
| |
|
| |
|
| |
| ===Development===
| |
| Create an application. Application requirements:
| |
| *The module needs to define a <code>__main__ </code>
| |
| *<code>cherrypy.quickstart(<Application Name>())</code> for hosting a single application. For example: cherrypy.quickstart(Blog())
| |
| *<code>cherrypy.tree.mount(<Application Name>(), ‘/<hosting path segment>’, <configuration>)</code> for hosting multiple applications. For example: <code>cherrypy.tree.mount(Blog(), ‘/blog’, blog_conf) </code>
| |
| *All parts the users will see must be exposed with either the decorator <code>@cherrypy.expose or attribues exposed = True</code> or <code>route.exposed = True.</code>
| |
|
| |
| <pre>
| |
| import cherrypy
| |
| class HelloWorld(object):
| |
| def index(self):
| |
| return “Hello World!”
| |
| index.exposed = True
| |
| if __name__ == ‘__main__’:
| |
| cherrypy.quickstart(HelloWorld())
| |
| </pre>
| |
|
| |
| ===Deployment===
| |
| The application can be run as a python script in the Python interpreter.
| |
| $ python <app file>.py
| |
| It will hosted at http://127.0.0.1:8080/
| |
| It can also be run as a daemon process with
| |
| $cherryd -c <config file> -d -p <PID file>
| |
|
| |
| ==Testing==
| |
| CherryPy provides a helper class for testing. The feature of the framework is that test are run against a running cherrypy server and testing small cmponents without actually starting the server is not natively suported.
| |
|
| |
| Lets look at an example<ref>http://cherrypy.readthedocs.org/en/latest/advanced.html#testing-your-application</ref>
| |
|
| |
| <pre>
| |
| #importing cherrypy library
| |
| import cherrypy
| |
|
| |
| #importing the helper class
| |
| from cherrypy.test import helper
| |
|
| |
| #creating a simple test class
| |
| class SimpleCPTest(helper.CPWebCase):
| |
|
| |
| # function to start the cherrypy server
| |
| def setup_server():
| |
|
| |
| # root class of application to be tested
| |
| class Root(object):
| |
|
| |
| # the expose method which we are trying to test
| |
| # this method will respond to localhost/echo and actually echo the argument sent to it
| |
| @cherrypy.expose
| |
| def echo(self, message):
| |
| return message
| |
|
| |
| # settingup the root class to be created on server start
| |
| cherrypy.tree.mount(Root())
| |
|
| |
| # grabbing the decorator for starting the server
| |
| setup_server = staticmethod(setup_server)
| |
|
| |
| # This is the actual test code
| |
| def test_message_should_be_returned_as_is(self):
| |
|
| |
| # sending arguments to the echo method via html request
| |
| self.getPage("/echo?message=Hello%20world")
| |
|
| |
| # chechink if server accepted our request
| |
| self.assertStatus('200 OK')
| |
|
| |
| # cheching response from server
| |
| self.assertHeader('Content-Type', 'text/html;charset=utf-8')
| |
|
| |
| # checking if the was an "Hello World" in the response from server
| |
| self.assertBody('Hello world')
| |
|
| |
| </pre>
| |
|
| |
| ==Extensions==
| |
|
| |
| CherryPy provides a flexible open framework. Similar to [http://en.wikipedia.org/wiki/RubyGems RubyGems] in [http://en.wikipedia.org/wiki/Ruby_on_Rails Ruby on Rails] which add a range of functionality to the framework CherryPy also supports plugins in the the following forms
| |
|
| |
| ===Server Wide Functions (Plugins)===
| |
| This type of extension is typically used to provide the application server itself with additional functionality. Such functions are executed with respect to events in the server even when there is no client request processing taking place.<ref>http://docs.cherrypy.org/en/latest/extend.html#id13</ref><br/>
| |
| Typical use case involve
| |
| *Background Tasks (Tasks which involve server mentainance, data management etc. which are independent of user requests)
| |
| *External Connections (For establishing and maintaining threaded connections to external database or other servers)
| |
| *Delayed/Queued Processing (Cases when certain tasks are required by the user request which take a long time process and the HTTP response should not be blocked.)<br/>
| |
| These function utilize the [http://en.wikipedia.org/wiki/Publish–subscribe_pattern Publish-Subscribe Framework] implementation of CherryPy. Each function subscribes to one or more events on the bus which are published by the CherryPy engine.<br/> The database connection is a good example of such a function<br/>
| |
|
| |
| <pre>
| |
| # import the Handles
| |
| import MySQLdb
| |
| import cherrypy
| |
| # defining the connection function
| |
| def connect(thread_index):
| |
| # Create a connection and store it in the current thread
| |
| cherrypy.thread_data.db = MySQLdb.connect('host', 'user', 'password', 'dbname')
| |
|
| |
| # tell cherrypy to call connect function for each thread
| |
| cherrypy.engine.subscribe('start_thread', connect)
| |
| </pre>
| |
|
| |
| Here the function connect subscribes to the <code>start_thread</code> channel. An event is published on the <code>start_thread</code> channel whenever a server thread is started. Here <code>engine</code> is the central bus of the CherryPy server.<br/>
| |
| Similarly it is also possible to create new channels and even buses themselves.
| |
|
| |
| ===Per-Request Functions (Tools)===
| |
| This type of extension is typically used to insert functionality between stages of request processing. Also known as [http://docs.cherrypy.org/en/latest/extend.html#tools Tools] these are simple call-back functions registered with a [http://docs.cherrypy.org/en/latest/extend.html#hookpoint Hook Point]. Hook Points are predefined stages of request processing. CherryPy provides a [http://tools.cherrypy.org/ Default ToolBox] containing many tools. Users have the freedom to create their own tools and add them to the default toolbox or create a new one.<ref>http://docs.cherrypy.org/en/latest/extend.html#per-request-functions</ref><br/>
| |
| An example for creating a tool
| |
|
| |
| <pre>
| |
| # defining the function to be called
| |
| def my_tool():
| |
| # put tool functunality here
| |
| print (“Super Amazing Tool”);
| |
|
| |
| # creating the decorator for the tool
| |
| # specifying the hook point and function to be called
| |
| cherrypy.tools.mytool = cherrypy.Tool(‘on_end_request’, my_tool())
| |
|
| |
| #Sample Usage
| |
|
| |
| class Root(object):
| |
| @cherrypy.expose()
| |
| @cherrypy.tools.mytool()
| |
| def index()
| |
| return “Hello World”
| |
| </pre>
| |
|
| |
| ==Watch It In Action==
| |
|
| |
| CherryPy is used as a building block for [http://www.hulu.com/ Hulu]<ref>http://tech.hulu.com/blog/2013/03/13/python-and-hulu</ref> and [https://www.netflix.com/ Netflix]<ref>http://techblog.netflix.com/2013/03/python-at-netflix.html</ref>
| |
|
| |
| ==Further Reading==
| |
| [https://docs.google.com/presentation/d/1NOGM5w1yu6dnXyEyYC4r6ZDuRgii4YaqlkrrlxfbnzM/edit?pli=1#slide=id.p PowerPoint Presentation]
| |
|
| |
|
| |
|
| ==References== | | ==References== |
| <references/> | | <references/> |
