Wednesday, June 23, 2010

Lambda functions in Python

Using lambda functions in python. Defining a lambda function

Lambda functions in python can be somewhat confusing. Here is a brief introduction

Lambda functions are handy functions that can be defined in 1 line, and thrown away afterwards. Here is a small example of what the syntax for a normal function looks like, and what the syntax for a lambda function looks like:

def f(x): return x * x

And here is the same function using the lambda syntax:

f = lambda x : x * x

Lambda functions really come in handy when used with python functions such as filter(), map() and reduce(). Here are some examples.

First we have filter. It will return a copy of a list where the function you pass returns True. This example will return only even numbers (because any number mod 2 will be equal to 0 if it is even).

array = [1, 2, 3, 4, 5, 6] #create an array of integers
print filter(lambda x: x % 2 == 0, array)


[2, 4, 6] # a list containing all even numbers

Next we will show map. It is basically a mapping of one list to another using a function (or a lambda function):

array = [1, 2, 3, 4, 5, 6] #create an array of integers
print map(lambda x: x * x, array)


[1, 4, 9, 16, 25, 36] # a list containing squares of 1, 2, 3, etc

And finally we have reduce. What this will do is convert the list into a single value. Our function will add element 0 and element 1. That result is then added to element 3, that result is then added to element 4, etc. Eg. (((((1+2) + 3) + 4) + 5) + 6) = 21

array = [1, 2, 3, 4, 5, 6] #create an array of integers
print reduce(lambda x, y: x + y, array)



And that concludes our short tutorial on creating and using lambda functions

Python: Defining a function.

Defining a function in python

Python function definitions are simple. Defining a function in python is very similar to many other languages out there. Lets try it out:

def hello(x) :
print "Hello", x


Output is as follows

Hello Bill

Notice we used print with a comma. This allows concatenation of strings in a single line statement.

An interesting property of functions in python is that you are able to assign them to variables.

variable1 = hello # assigns the variable "variable1" to the function we created above "hello"

Will output

Hello Sarah

That is all for now. Thanks and please add comments.

Monday, June 21, 2010

Technology Behind Facebook OSS Open Source

Facebook and OSS server software and hardware setup

The software and hardware behind facebook

Love it or hate it, facebook has some great, open source software behind it. It has also contributed to the open source movement quite a bit. Here is an article I found interesting.

Monday, June 14, 2010

Facebook Chat in Empathy Ubuntu Linux

Using Facebook Chat in Ubuntu on Empathy

Facebook Chat Server Settings:

To set up the configuration:

Click edit->accounts, then click the Add button.

  • Account Type: Jabber

  • Reuse existing account

  • Create

  • Login ID: <username> (Note you must create a facebook username if you have not already)

  • Under Advanced - Server:

Then you are finished. Make sure SSL is disabled (which should be the default). Please leave some comments! Thanks!