To create a Modules in Python, you use the def keyword, followed by the function name and argument list, and a colon to begin the function body.

General Syntax :

def (argument_list):
....}=> Body

P.S : Indentation must be taken care

Ok , now lets see few eliminator examples of modules .

import sys

def main():
print "\nTill which level do you want to see the sequence ? "
n = int(sys.stdin.readline()) # read from the user 
fibonacci(n) # call to the method with parameter 


def fibonacci(n):
a,b = 0,1
for i in range(0,n):
print a
a,b, = b,a+b

if __name__ == '__main__':
main()

Here the main method , calls the Fibonacci method , which prints the sequence of Fibonacci numbers.


A method can "RETURN" ?

As Python passes all arguments using "pass by reference" , the changes on the arguments in the method is always reflected on them .

A module can return an kind of data types , those which we had seen in the earlier post .

Keeping this in mind , here a small code which everything clear :

a, b, c = 0, 0, 0
def Giveabc():
a = "Hello"
b = "Python"
c = "!"
return a,b,c #defines a tuple on the fly

def GiveTuple():
a,b,c = 1,2,3
return (a,b,c)

def GiveList():
a,b,c = (3,4),(4,5),(5,6)
return [a,b,c]

a,b,c = Giveabc():
d,e,f = GiveTuple():
g,h,i = GiveList():

Different variations can be used to return what is required, based on our need :)


Lambda Expressions (Anonymous Functions) !!!

"In Python you can define a one-line mini-functions on the fly.
Borrowed from Lisp, these so-called lambda functions can be used anywhere a function is required."

The below is an wonderful example from the book "Dive Into Python".

>>> def f(x):
...     return x*2
...     
>>> f(3)
6
>>> g = lambda x: x*2  
>>> g(3)
6
>>> (lambda x: x*2)(3) 
6

I had to borrow it from there because, this is the best way we can know how lambda function can be really useful for us , in a simple one-line.