Snippets Archives - Grainier Perera

Simple Chat Application Using Jaggery Framework

In this blog post, it’s going to guide you through the steps which involve in creating a simple chat application using WSO2‘s Jaggery Framework.

What is Jaggery?

Jaggery is a framework, which offers a completely Javascript way to write all parts of Web applications and services as a way to minimize impedance mismatches across different layers of the Web application and API development experience while closing the gap between Web apps from Web services by allowing one to create both applications and APIs at the same time.

Functionality of the Chat Application

In this tutorial, it will only focus on providing these basic requirements for the Chat application.

Create a chat room with a unique id.
Join existing chat-room using it’s unique id.
Have multiple chat rooms opened in multiple tabs.
Kick off users from the chat room.

Continue reading Simple Chat Application Using Jaggery Framework

How to create a Persistable Dictionary in Python

I came across a situation where I had to implement a Python class which can;

handle dynamic attributes
can be initialized with a dictionary
can be persisted on the local storage as a file
can be used as a dictionary as well as a object. ( allow both foo['key'] and foo.key to access its attributes )

So I came up with this Class. It inherits from python’s built in Dictionary class ( dict ). Therefore it can be initialized with an existing dictionary. And it also overrides __getattr__ __setattr__ __delattr__ . Therefore it can handle dynamic attributes and act as a dictionary as well as a object. Finally It uses Python’s cPickle to serialize and persist it self in the local storage.

import cPickle as pickle


class PersistableDictionary(dict):
    __getattr__ = dict.__getitem__
    __setattr__ = dict.__setitem__
    __delattr__ = dict.__delitem__

    def __init__(self, name, **dictionary):
        self.name = name
        if not dictionary:
            dictionary = self.load()
        super(PersistableDictionary, self).__init__(**dictionary)
        pass

    def load(self):
        try:
            pkl_file = open('{}.pkl'.format(self.name), 'rb')
            data = pickle.load(pkl_file)
            pkl_file.close()
            pass
        except IOError, e:
            data = {}
            pass
        return dict(data)
        pass

    def save(self):
        output = open('{}.pkl'.format(self.name), 'wb')
        pickle.dump(dict(self), output)
        output.close()
        pass

    pass


if __name__ == '__main__':
    # initialize
    pd = PersistableDictionary("my_dict")

    # use as a normal dictionary
    pd['key_x'] = "value x"
    pd['key_y'] = "value y"

    # persist the dictionary
    pd.save()

    pd_copy = PersistableDictionary("my_dict")
    # acting as a dictionary
    for k in pd_copy:
        print "key : {} | value : {}".format(k, pd_copy[k])

    # acting as a object
    print "value of {} is : {}".format("pd.key_x", pd.key_x)
    print "value of {} is : {}".format("pd.key_y", pd.key_y)
    pass

import cPickle as pickle

class PersistableDictionary(dict):

__getattr__ = dict.__getitem__

__setattr__ = dict.__setitem__

__delattr__ = dict.__delitem__

def __init__(self, name, **dictionary):

self.name = name

if not dictionary:

dictionary = self.load()

super(PersistableDictionary, self).__init__(**dictionary)

pass

def load(self):

try:

pkl_file = open('{}.pkl'.format(self.name), 'rb')

data = pickle.load(pkl_file)

pkl_file.close()

pass

except IOError, e:

data = {}

pass

return dict(data)

pass

def save(self):

output = open('{}.pkl'.format(self.name), 'wb')

pickle.dump(dict(self), output)

output.close()

pass

if __name__ == '__main__':

# initialize

pd = PersistableDictionary("my_dict")

# use as a normal dictionary

pd['key_x'] = "value x"

pd['key_y'] = "value y"

# persist the dictionary

pd.save()

pd_copy = PersistableDictionary("my_dict")

# acting as a dictionary

for k in pd_copy:

print "key : {} | value : {}".format(k, pd_copy[k])

# acting as a object

print "value of {} is : {}".format("pd.key_x", pd.key_x)

print "value of {} is : {}".format("pd.key_y", pd.key_y)

pass

Please share your thoughts on this approach. 🙂

Iterate and Initialize all sub classes in python

In various situations, we need a mechanism to Initialize all Sub classes for a given Super class. For instance, let’s assume that we have a Super class called ArithmeticOperation and another 4 classes derived from it (Addition, Subtraction, Multiplication and Division).

class ArithmeticOperation(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def compute(self):
        # overload this method to compute
        pass
    pass


class Addition(ArithmeticOperation):
    def compute(self):
        result = self.x + self.y
        print "Addition : {}".format(result)
        pass
    pass


class Subtraction(ArithmeticOperation):
    def compute(self):
        result = self.x - self.y
        print "Subtraction : {}".format(result)
        pass
    pass


class Multiplication(ArithmeticOperation):
    def compute(self):
        result = self.x * self.y
        print "Multiplication : {}".format(result)
        pass
    pass


class Division(ArithmeticOperation):
    def compute(self):
        result = float(self.x) / float(self.y)
        print "Division : {}".format(result)
        pass
    pass

class ArithmeticOperation(object):

def __init__(self, x, y):

self.x = x

self.y = y

def compute(self):

# overload this method to compute

pass

class Addition(ArithmeticOperation):

def compute(self):

result = self.x + self.y

print "Addition : {}".format(result)

pass

class Subtraction(ArithmeticOperation):

def compute(self):

result = self.x - self.y

print "Subtraction : {}".format(result)

pass

class Multiplication(ArithmeticOperation):

def compute(self):

result = self.x * self.y

print "Multiplication : {}".format(result)

pass

class Division(ArithmeticOperation):

def compute(self):

result = float(self.x) / float(self.y)

print "Division : {}".format(result)

pass

One way of doing it is Initializing each Sub class separately.

if __name__ == '__main__':
    num_1 = 20
    num_2 = 10

    a = Addition(num_1, num_2)
    a.compute()

    s = Subtraction(num_1, num_2)
    s.compute()

    m = Multiplication(num_1, num_2)
    m.compute()

    d = Division(num_1, num_2)
    d.compute()

if __name__ == '__main__':

num_1 = 20

num_2 = 10

a = Addition(num_1, num_2)

a.compute()

s = Subtraction(num_1, num_2)

s.compute()

m = Multiplication(num_1, num_2)

m.compute()

d = Division(num_1, num_2)

d.compute()

But if there are hundreds of Sub classes, we need to think of another mechanism. That’s where .__subclasses__() becomes very useful. We can use that method to Iterate and Initialize all Sub classes for that given Super Class. You can do it like this,

if __name__ == '__main__':
    num_1 = 20
    num_2 = 10

    for Operation in ArithmeticOperation.__subclasses__():
        factor = Operation(num_1, num_2)
        factor.compute()
    pass

if __name__ == '__main__':

num_1 = 20

num_2 = 10

for Operation in ArithmeticOperation.__subclasses__():

factor = Operation(num_1, num_2)

factor.compute()

pass

Hope this post helped someone who’s looking for a way to Iterate and Initialize all Sub classes for a given Super Class using python. 🙂

How to use ( set, get, delete ) cookies in JavaScript

In this post you can find to how to set, get (retrieve) and delete cookies using JavaScript. This might comes in handy when you want to securely store small amount in the client side.

var cookie = new function() {
    this.set = function ( name, value, days ) {
        var expires = "";
        if ( days ) {
            var date = new Date();
            date.setTime( date.getTime() + ( days * 24 * 60 * 60 * 1000 ) );
            expires = "; expires=" + date.toGMTString();
        }
        document.cookie = name + "=" + value + expires + "; path=/";
    };

    this.get = function ( name ) {
        var nameEQ = name + "=";
        var ca = document.cookie.split( ';' );
        for ( var i = 0; i < ca.length; i++ ) {
            var c = ca[ i ];
            while ( c.charAt(0) == ' ' ) c = c.substring( 1, c.length );
            if ( c.indexOf( nameEQ ) == 0 ) return c.substring( nameEQ.length, c.length );
        }
        return null;
    };

    this.delete = function ( name ) {
        this.set( name, "", -1 );
    };
}

// set a cookie
cookie.set( 'sitename', 'http://grainier.net', 2 );

// retrieve a cookie
var sitename = cookie.get( 'sitename' );
alert( sitename );

// delete a cookie
cookie.delete( 'sitename' );

var cookie = new function() {

this.set = function ( name, value, days ) {

var expires = "";

if ( days ) {

var date = new Date();

date.setTime( date.getTime() + ( days * 24 * 60 * 60 * 1000 ) );

expires = "; expires=" + date.toGMTString();

}

document.cookie = name + "=" + value + expires + "; path=/";

};

this.get = function ( name ) {

var nameEQ = name + "=";

var ca = document.cookie.split( ';' );

for ( var i = 0; i < ca.length; i++ ) {

var c = ca[ i ];

while ( c.charAt(0) == ' ' ) c = c.substring( 1, c.length );

if ( c.indexOf( nameEQ ) == 0 ) return c.substring( nameEQ.length, c.length );

}

return null;

};

this.delete = function ( name ) {

this.set( name, "", -1 );

};

}

// set a cookie

cookie.set( 'sitename', 'http://grainier.net', 2 );

// retrieve a cookie

var sitename = cookie.get( 'sitename' );

alert( sitename );

// delete a cookie

cookie.delete( 'sitename' );

Working example : click here

Shuffle an array in javascript

This code snippet can be use to Shuffle an array in JavaScript.

function shuffleArray ( array ) {
    var counter = array.length, temp, index;
    // While there are elements in the array
    while ( counter > 0 ) {
        // Pick a random index
        index = Math.floor( Math.random() * counter );

        // Decrease counter by 1
        counter--;

        // And swap the last element with it
        temp = array[ counter ];
        array[ counter ] = array[ index ];
        array[ index ] = temp;
    }
    return array;
}

var originalArray = [ 'a', 'b', 'c', 'd' ];
var shuffledArray = shuffleArray( originalArray );

function shuffleArray ( array ) {

var counter = array.length, temp, index;

// While there are elements in the array

while ( counter > 0 ) {

// Pick a random index

index = Math.floor( Math.random() * counter );

// Decrease counter by 1

counter--;

// And swap the last element with it

temp = array[ counter ];

array[ counter ] = array[ index ];

array[ index ] = temp;

}

return array;

}

var originalArray = [ 'a', 'b', 'c', 'd' ];

var shuffledArray = shuffleArray( originalArray );

working example : http://jsfiddle.net/grainier/J4BuD/