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)

Output:

[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)

Output:

[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)

Output:

21

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

hello("Bill")

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"
variable1("Sarah")

Will output

Hello Sarah

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

PHP's case sensitivity in function names

Hi Everyone,

Just thought I'd toss out a random tidbit. I've found a program that tried to define a function name that conflicted with a global function name, but not like you would expect.

They used camel case for the function name, when the system defined function didn't. Unfortunately function names in PHP are NOT case sensitive, as shown in the following experiment:

<?php

function test_func() {
        echo 'test_func';
}

function Test_Func() {
        echo 'Test_Func';
}

Running this script gives:

bill-hamiltons-imac:~ bill$ php test.php 

Fatal error: Cannot redeclare test_func() (previously declared in /Users/bill/test.php:4) in /Users/bill/test.php on line 9

So there you have it. PHP function names are not case sensitive which some of you may already know but this is obviously the proof.

Thanks!