Chapter Functions for grade 12 computer Science

Function Introduction
A function is a subprogram that acts on data and often returns a value
OR
A function is a programming block of codes which is used
1. to perform a single, related task.
2. It only runs when it is called.
3. We can pass data/value, known as parameters, into a function.
4. A function can return data as a result.

Advantages of Using Functions:
1.Program development made easy and fast : Work can be divided among
project members thus implementation can be completed fast.
2. Program testing becomes easy
3. Code sharing becomes possible
4.Code re-usability increases
5. Increases program readability
6.Function facilitates procedural abstraction : Once a function is written,
it serves as a black box. All that a programmer would have to know to invoke a
function would be to know its name, and the parameters that it expects
7.Functions facilitate the factoring of code : A function can be called in
other function and so on…

• Built –in functions (function using Libraries)
• Functions defined in the modules(function using Libraries)
• User defined functions
Types of Functions

Built-in functions
Pre-defined functions that are always available
for use.
e.g.
print() ,len() ,input() ,ord() ,hex() ,type(), int() etc

String functions:
Method Description
isalnum() Returns True if all characters in the string are alphanumeric
isalpha() Returns True if all characters in the string are in the alphabet
isdecimal() Returns True if all characters in the string are decimals
isdigit() Returns True if all characters in the string are digits
islower() Returns True if all characters in the string are lower case
isnumeric() Returns True if all characters in the string are numeric
isspace() Returns True if all characters in the string are whitespaces
istitle() Returns True if the string follows the rules of a title
isupper() Returns True if all characters in the string are upper case
lower() Converts a string into lower case
lstrip() Returns a left trim version of the string
partition() Returns a tuple where the string is parted into three parts
Functions using libraries(System defined function or Built- in Functions)
Syntax:
stringname.functionname()
e.g.
a.isupper()

String functions:
Method Description Syntax
capitalize() Converts the first character to upper case str.capitalize()
center() string padded with specified fillchar. str.center(width,[fillchar])
#Width means length of the string
count() Returns the number of times a specified value
occurs in a string
str.count(substring,[start], [end])
endswith() Returns true if the string ends with the
specified value
str.endswith(substring,[start],[end])
format() Formats specified values in a string print("Hello {}, your rollno {}.".format(“abc", 23))
print("Hello {name}, your rollno {rn}.“
.format(name=“abc", rn=23))
find()
Searches the string for a specified value and
returns the position(index) of where it was
found
str.find(sub,[start],[end] )
index()
Searches the string for a specified value and
returns the position of where it was found
str.index(sub,[start],[end] )
The only difference is that find() method returns -1 if the substring is not found, whereas index() throws an exception.

String functions:
Method Description
replace()
Returns a string where a specified value is replaced with a
specified value
split() Splits the string at the specified separator, and returns a list
splitlines() Splits the string at line breaks and returns a list
startswith() Returns true if the string starts with the specified value
swapcase() Swaps cases, lower case becomes upper case and vice versa
title() Converts the first character of each word to upper case
upper() Converts a string into upper case
zfill() Fills the string with a specified number of 0 values at the beginning

Functions defined in modules
Pre-defined functions that are in particular
modules and can only be used when
corresponding module is imported.
e.g.
import math
sin(), cos(),abs(),floor() etc

Modules
Modules
• is a part of a program
• used for dividing up the program into smaller, more easily
understood, reusable parts.
A module is a file containing
1. Python definitions and statements.
2. Module can define functions, classes and variables.
3. A module can also include runnable code.
4. Grouping related code into a module makes the code easier to
understand and use.

Functions using libraries/ Functions defined in Modules
Mathematical functions:
Mathematical functions are available under math module.To use
mathematical functions under this module, we have to import the
module using import math.
For e.g.
To use sqrt() function we have to write statements like given below.
import math
r=math.sqrt(4)
print(r)
OUTPUT :
2.0

Functions available in Python Math Module
Functions using libraries(Functions defined in Modules)

User defined functions
These are defined by the programmer according
to his/her requirements /needs.

Creating a Function (user defined)
A function is defined using the def keyword in
python.
def <function_name>([arguments/parameters]):
[“”” function’s docstring “””]
<statement>
[statement]
[statement]
:
:
Function block/ definition/ working of the function
def fun():
print("Hello")
print(“world”)
e.g.
Syntax: Name of the function
colon at the end means it requires a block
def
means
function
definition
is starting
arguments/parameters-means values given to function
def cals(a):
b=2*a
print(b)

Few terms : Defining functions
• Function header- first line of the function that begins with the
keyword def and end with the (:) colon. It specifies the name of the
function and its parameters
• Parameters-values that are listed within the parentheses of a
function header
• Indentation- blank space in the beginning of a statement within a
block. All statements within the block have same indentation.

Calling a Function(user defined)
Syntax:
def Function_name(arguments/parameters):
statements
#program start here.program code
print("hello before calling a function")
fun(3) #function calling.now function codes will be executed
print("hello after calling a function")
def fun(a):
print(“hello”,a)
Function definition

4 Parts To Create User Defined Functions
•Function definition
•Arguments(those variables which
are use in function calling)
•Parameters(those variables which
are use in function definition)
•Function Calling

Flow of execution in function Calling
• 1 def fun(a,b):
• 2 c=a+b
• 3 print(c)
• 4 x=2
• 5 y=4
• 6 fun(x,y)
1-4-5-6-1-2-3
void functions- those functions which are not
returning values to the calling function

• 1 def fun(a,b):
• 2 c=a+b
• 3 return c
• 4 x=int(input())
• 5 y= int(input())
• 6 z=fun(x,y)
• 7 print(z)
1-4-5-6-1-2-3-6-7
Non void functions- those functions which are
returning values to the calling function

1.def fun(a,b):
2. c=a+b
3. print(c)
4. return
5.x=2
6.y=4
7.z=fun(x,y)
8.print(z)
1-5-6-7-1-2-3-4-8
Void functions- those functions which are not
returning values to the calling function.
We may use return but it will return none value to the
function call

Void functions and Non void functions
def fun(a,b):
c=a+b
print(c)
return
x=2
y=4
z=fun(x,y)
print(z)
We may use return but it will
return none value to the
function call
def fun(a,b):
return a+b, a, 5
x=2
y=4
z,w,q=fun(x,y)
print(z,w,q)
Output
6
None
Output
6 2 5
Value return can be literal,variable ,
expression

Arguments/Parameters
def fun(a,b):
c=a+b
print(c)
x=2
y=4
fun(x,y) #variables
fun(5,6) #literals
fun(x+3,y+6) #expressions
Arguments- passed values in function call.
It can be of three types
1. Literals
2. Variables
3. Expressions
Arguments

Arguments/Parameters
def fun(a,b): #parameters
c=a+b
print(c)
x=2
y=4
fun(x,y)
Parametes- received values in function
definition.
It should be of variable types.

Returning Multiple Values from Functions
def fun(a,b):
return a+b,a-b
x=2
y=4
z=fun(x,y)
print(z)
1. Received values as tuple
2. Unpack received values as tuple
def fun(a,b):
return a+b,a-b
x=2
y=4
d,z=fun(x,y)
print(d,z)

def fun(x,y): #Parameters- variables used in function definition - should be of variable type here x and y are parameters
z=x+y
return z, z**3 ,5 #function can return values in the form of variable, expression, literal
#function calling
a=int(input("enter no1")) #1 a=4
b=int(input("enter no2")) #2 b=5function calling
q=fun(a,b) #variable type arguments (values which are used in function calling)
print(q)
t=fun(3,5) #literal type arguments here 3 and 5 are literal type arguments
print(t)
z=fun(a+3,b+4) #expression type arguments
print(z)
‘’’
Output
enter no1 5
enter no2 6
(11, 1331, 5)
(8, 512, 5)
(18, 5832, 5)
‘’’
Here output is in the form of tuples
becoz function is returning multiple
values and we r storing them in single
variable

Returning Values from Functions
four possible combinations as functions
def fun():
a=2
b=3
print(a,b)
fun()
1. Void functions without arguments
2. Void functions with arguments
def fun(a,b):
print(a+b)
x=2
y=3
fun(x,y)

Returning Values from Functions
four possible combinations as functions
def fun():
a=2
b=3
return(a,b)
c=fun()
print(c)
3. Non Void functions without arguments
4. Non Void functions with arguments
def fun(a,b):
return(a+b)
x=2
y=3
c=fun(x,y)
print(c)

Types of Arguments
def fun(a,b):
c=a+b
print(c)
x=10
y=3
fun(x,y)
fun(x,y,z) #wrong no of arguments passed
1. Positional parameters(Required Arguments) - these arguments
must be provided for all parameters

Types of Arguments
def fun(a,b,c=3):
d=a+b+c
print(d)
x=10
y=3
fun(x,y) #here c parameter value is 3
z=5
fun(x,y,z) #here it will be take parameter c value as 5
2. Default Arguments- if right parameter have default value then left parameters can
also have default value. this argument can be skipped at the time of function calling

Types of Arguments
def fun(a,b,c):
print(a,b,c)
a=1
b=3
c=5
fun(b,c,a)
3. Keyword Arguments(Named Arguments)- We can write arguments in any
order but we must give values according to their name
Output
3 5 1
def fun(a,b,c):
print(a,b,c)
fun(b=3,c=4,a=2)
Output
2 3 4

Scope of Variables
Scope means –to which extent a code or data would be known or accessed.
There are three types of variables with the view of scope.
1. Global Scope- Name declared in main program . It is usable inside the whole
program.
def fun(a,b):
s = a+b
print(s)
X=int(input(“enter no1”))
Y=int(input(“enter no2”))
fun(X,Y)
#here X and Y are global variable
def fun(a):
s = a+Y
retrun(s)
X=10
Y=20
Z=fun(X,Y)
Print(Z)
#here X and Y are global variable

Scope of Variables
Scope means –to which extent a code or data would be known or accessed.
1. Local Scope- Name declared in function body. It is usable within the function.
def fun():
A=10
B=20
return(A+B)
C=fun()
print(C)
print(A)
#here A and B are local variables and C is
global varibale

Variable’s Scope in function
.
1. Non local variable – accessible in nesting of functions,using nonlocal keyword.
def fun1():
x = 100
def fun2():
nonlocal x #change it to global or remove this declaration
x = 200
print("Before calling fun2: " + str(x))
print("Calling fun2 now:")
fun2()
print("After calling fun2: " + str(x))
x=50
fun1()
print("x in main: " + str(x))
OUTPUT:
Before calling fun2: 100
Calling fun2 now:
After calling fun2: 200
x in main: 50

Variable’s Scope in function
There are three types of variables with the view of scope.
1. Local variable – accessible only inside the functional block where it is declared.
2. Global variable – variable which is accessible among whole program using
global keyword.
3. Non local variable – accessible in nesting of functions,using nonlocal keyword.
Local variable program:
def fun():
s = "I love India!" #local variable
print(s)
s = "I love World!"
fun()
print(s)
Output:
I love India!
I love World!
Global variable program:
def fun():
global s #accessing/making global variable for fun()
print(s)
s = "I love India!“ #changing global variable’s value
print(s)
s = "I love world!"
fun()
print(s)
Output:
I love world!
I love India!
I love India!

Name Resolution
.
Resolving Scope of a name: LEGB Rule
1. Local
2. Enclosed
3. Global
4. Built in
.
def fun1(x,y):
s=x+y
print(num1)
return s
num1=100
num2=200
sm=fun1(num1,num2)
print(sm)
.
Variable in global scope not in local scope
CASE 1

Name Resolution
.
1. Local
2. Enclosed
3. Global
4. Built in
.
def fun():
print(“hello”,n)
fun()
#
Output:
Name error: name ‘n’ is
not defined
.
Variable neither in in local scope nor in global scope
CASE 2

Name Resolution
.
1. Local
2. Enclosed
3. Global
4. Built in
.
def fun():
a=10
print(a)
a=5
print(a)
fun()
print(a)
# output
5
10
5
.
Variable name in local scope as well as in global scope
CASE 3

Name Resolution
.
1. Local
2. Enclosed
3. Global
4. Built in
.
def fun():
global a
a=10
print(a)
a=5
print(a)
fun()
print(a)
# output
5
10
10
.
Using global variable inside local scope
This case is discouraged in
good programming
CASE 4

Function
Parameters / Arguments
These are specified after the function name, inside the parentheses. Multiple
parameters are separated by comma.The following example has a function with
two parameters x and y. When the function is called, we pass two values, which
is used inside the function to sum up the values and store in z and then return
the result(z):
def sum(x,y): #x, y are formal arguments
z=x+y
return z #return the result
x,y=4,5
r=sum(x,y) #x, y are actual arguments
print(r)
Note :- 1. Function Prototype is declaration of function with name
,argument and return type.
2. A formal parameter, i.e. a parameter, is in the function definition. An
actual parameter, i.e. an argument, is in a function call.

Function Arguments
Functions can be called using following types of formal arguments −
• Required arguments - arguments passed to a function in correct positional order
• Keyword arguments - the caller identifies the arguments by the parameter name
• Default arguments - that assumes a default value if a value is not provided to argu.
#Required arguments/Positional arguments
def square(x):
z=x*x
return z
print(square(3)
#In above function square() we have to definitely need to
pass some value
#Keyword arguments
def fun( name, age ):
print (name,age)
return;
fun( age=15, name="mohak" )
# value 15 and mohak is being passed to
relevant argument based on keyword used for them.
#Default arguments
def sum(x=3,y=4):
z=x+y
return z
r=sum() #default value of x and y is being used when it is not passed
print(r)
r=sum(x=4)
print(r)
r=sum(y=45)
print(r)

Mutable/Immutable properties of data w/r function
Everything in Python is an object,and every objects in Python can be
either mutable or immutable.
Since everything in Python is an Object, every variable holds an object
instance. When an object is initiated, it is assigned a unique object id. Its
type is defined at runtime and once set can never change, however its
state can be changed if it is mutable.
Means a mutable object can be changed after it is created, and an
immutable object can’t.
Mutable objects: list, dict, set, byte array
Immutable objects: int, float, complex, string, tuple, frozen set ,bytes

Passing Immutable type values to a function
e.g.
def fun(a):
print(a)
a=a+2
print a
n=3
print(n)
fun(n)
print(n)
Output
3
3
5
3
Passed value of n remains unchanged because it is immutable

Passing mutable type value to a function
e.g.
def fun(a):
print(a)
a[0]=1
print (a)
n=[3,5,6]
print(n)
fun(n)
print(n)
Output
3,5,6
3,5,6
1,5,6
1,5,6
Value changed in function change the value in main program(because list
change values at same address and only single value is changing)
CASE-1

Passing mutable type value to a function
e.g.
def fun(a):
print(a)
f=[7,8]
a=f
print (a)
n=[3,5,6]
print(n)
fun(n)
print(n)
Output
3,5,6
3,5,6
7,8
3,5,6
Value changed in function did not change for main program(because a is
assigned a whole new list not a change of single values for whole
program
CASE-2

Pass Mutable type values to a function
Arrays are popular in most programming languages like: Java, C/C++, JavaScript and
so on. However, in Python, they are not that common. When people talk about Python
arrays, more often than not, they are talking about Python lists. Array of numeric
values are supported in Python by the array module.
e.g.
def dosomething( thelist ):
for element in thelist:
print (element)
dosomething( ['1','2','3'] )
alist = ['red','green','blue']
dosomething( alist )
OUTPUT:
1
2
3
red
green
Blue
Note:- List is mutable datatype that’s why it treat as pass by reference.It is
already explained in topic Mutable/immutable properties of data objects w/r
function

Mutable/immutable properties of data objects w/r function
How objects are passed to Functions
#Pass by reference
def updateList(list1):
print(id(list1))
list1 += [10]
print(id(list1))
n = [50, 60]
print(id(n))
updateList(n)
print(n)
print(id(n))
OUTPUT
34122928
34122928
34122928
[50, 60, 10]
34122928
#In above function list1 an object is being passed
and its contents are changing because it ismutable
that’s why it is behaving like pass by reference
#Pass by value
def updateNumber(n):
print(id(n))
n += 10
print(id(n))
b = 5
print(id(b))
updateNumber(b)
print(b)
print(id(b))
OUTPUT
1691040064
1691040064
1691040224
5
1691040064
#In above function value of variable b is not
being changed because it is immutable that’s
why it is behaving like pass by value

Chapter Functions for grade 12 computer Science

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