The document introduces functions in Python, explaining their significance in structuring programs and reusing code. It details the syntax for defining a function, including the return statement and handling arbitrary parameters. The document also provides examples demonstrating the use of functions and additional resources for further learning.

1. Python for ethical hackers
Mohammad reza Kamalifard
kamalifard@datasec.ir

2. Python language essentials
Module 1:
Introduction to Python and Setting up an Environment for Programing
Part 5 :
Functions

3. Functions
• Functions are a construct to structure programs.
• Functions are used to utilize code in more than one place
in a program.
• The only way without functions to reuse code consists in
copying the code.

4. Functions
• Functions allow sections of code to be grouped better as
per functionality

5. Functions
A function in Python is defined by a def statement. The
general syntax looks like this:
def function-name(Parameter list):
statements, i.e. the function body
• The parameter list consists of none or more parameters.
• The function body gets executed every time the function is
called.

6. Functions
def function(arg1,arg2=default,..):
do_something
return value
>>> def print5times(input):
...
for count in range(0,5):
...
print input
...
>>> print5times('Hello')
Hello
Hello
Hello
Hello
Hello

7. >>> print5times('Javad')
Javad
Javad
Javad
Javad
Javad
>>> print5times('Hello, World!')
Hello, World!
Hello, World!
Hello, World!
Hello, World!
Hello, World!
>>>

8. return statement
• Function bodies can contain a return statement.
• Can be anywhere in the function body.
• Ends the execution of the function call and "returns" the
result, i.e. the value of the expression following the return
keyword, to the caller.
• If there is no return statement in the function code, the
function ends, when the control flow reaches the end of the
function body.

9. def add(x, y):
"""Return x plus y"""
return x + y
>>> add(4, 5)
9
>>> add(8, 3)
11
>>>

10. def add(x, y = 5):
"""Return x plus y"""
return x + y
>>> add(4)
9
>>> add(8, 3)
11
>>>

11. Arbitrary Number of Parameters
def arbitrary(x, y, *more):
print "x=", x, ", x=", y
print "arbitrary: ", more
>>>arbitrary(3, 4)
x = 3 , x = 4
arbitrary: ()
>>>arbitrary(3, 4, "Hello World", 5 ,6)
x = 3 , x = 4
arbitrary: ('Hello World', 5, 6)

12. $ vim testargv.py
#!/usr/bin/env python
import sys
print sys.argv
~
~

13. $ chmod a+x testargv.py
$ ./testargv.py
['./testargv.py']
$
$ ./testargv.py salam
['./testargv.py', 'salam']
$
$
$./testargv.py -h 199 --app firefox
['./testargv.py', '-h', '199', '--app', 'firefox']
$

14. $ ./function.py salam
salam
salam
salam
salam
salam
$
$ ./function.py salam hamid
salam
salam
salam
salam
salam
$
$ ./function.py 'salam hamid'
salam hamid
salam hamid
salam hamid
salam hamid
salam hamid

15. $ vim function.py
#!/usr/bin/env python
import sys
def print5times(content_to_print):
for count in range(0,5):
print content_to_print
print5times(sys.argv[1])
~
~

16. $ ./function.py salam
salam
salam
salam
salam
salam
$
$ ./function.py salam hamid
salam
salam
salam
salam
salam
$
$ ./function.py 'salam hamid'
salam hamid
salam hamid
salam hamid
salam hamid
salam hamid

17. References
SPSE securitytube training by Vivek Ramachandran
SANS Python for Pentesters (SEC573)
Violent python
Security Power Tools
python-course.eu
----------------------------http://www.python-course.eu/functions.php
http://www.tutorialspoint.com/python/python_functions.htm

18. This work is licensed under the Creative Commons Attribution-NoDerivs 3.0 Unported License.
To view a copy of this license, visit
http://creativecommons.org/licenses/by-nd/3.0/
Copyright 2013 Mohammad Reza Kamalifard
All rights reserved.
Go to Kamalifard.ir/pysec101 to Download Slides and Course martials .