functionfunctionfunctionfunctionfunction12.pdf

Computer Science
Chapter-1
K V C o d e r s
L E T ’ S C R A C K C B S E C O M U P T E R S C I E N C E
As Per CBSE
Syllabus
2022-23

K V C o d e r s
A Function is a set of codes that are design to perform a single or related task,
it provide modularity and increase code reusability. A function executes only
when t is being called. Python provides many build in function like print(),
len(), type()..etc, whereas the functions created by us, is called User Defined
Functions.
When a function is called for execution, Data can be passes to the function
called as function parameters. After execution the function may return data
from the function.
What is a Function?

K V C o d e r s
Benefits of using Function
• Code Reusability: A function once created can be called countless number of times.
• Modularity: Functions helps to divide the entire code of the program into separate
blocks, where each block is assigned with a specific task.
• Understandability: use of Functions makes the program more structured and
understandable by dividing the large set of codes into functions
• Procedural Abstraction: once a function is created the programmer doesn’t have to know
the coding part inside the functions, Only by knowing how to invoke the function, the
programmer can use the function.

K V C o d e r s
Types of Functions in Python
1. Built-in Function: Ready to use functions which are already defined in python and the
programmer can use them whenever required are called as Built-in functions. Ex: len(), print(),
type()..etc
2. Functions defined in Modules: The functions which are defined inside python
modules are Functions defined in modules. In order to use these functions the programmer
need to import the module into the program then functions defined in the module can be
used.
import math
math.pow(5,2)
To use the function pow(), first
we need to import the module
math, because pow() is #defined
inside the math module.

K V C o d e r s
3.User Defined Function
Functions that are defined by the programmer to perform a specific task is called as User
Defined Functions. The keyword def is used to define/create a function in python.
Defining a Function
Syntax:
Lets define our first user defined function:
def <Function Name>([parameters]):
body of the function
[statements]
def myFirstFunction ( a ):
print(“inside my first function”)
print(a)
myFirstFunction(“bye”)
Output:
Inside my first function
bye
Function Name
Function Argument
Function call

K V C o d e r s
Elements in Function Definition
• Function Header: The first line of the function definition is called as function header. The header start
with the keyword def, and it also specifies function name and function parameters. The header ends
with colon ( : ). def sum(a,b): #function Header
• Parameter: Variables that are mentioned inside parenthesis ( ) of the function Header.
• Function Body: The set of all statements/indented-statements beneath the function header that
perform the task for which the function is designed for.
• Indentation: All the statements inside the function body starts with blank space (convention is four
statements).
• Return statement: A function may have a return statement that is used to returning values from
functions. A return statement can also be used without any value or expression.

K V C o d e r s
Flow of Execution in a Function Call
#Function Definition
def myfun(x,y):
.
.
return
.
.
a=10
b=20
#function call
myfun(a,b)
print(…)
When a function is called the
programs control flow will
shift to the function
definition
After the last statement of the
function is executed or when a
return statement is encountered
the control flow will shift back to
the place from where the function
is called

K V C o d e r s
Arguments and parameters in Function
In Python, the variables mentioned withing parathesis () of a function definition are
referred as parameters(also as formal parameter/formal argument) and the variables
present inside parathesis of a function call is referred as arguments (also as actual
parameter/actual argument).
Python supports 4 types of parameters/formal arguments
1. Positional Argument
2. Default Argument
3. Keyword Argument
4. Variable length argument

K V C o d e r s
1.Positional Arguments:
When function call statement must contain the same number and order of arguments as
defined in the function definition, then the arguments are referred as positional argument.
def myfun(x,y,z):
[statements]
….
myfun(a,b,c)
myfun(a,8,9)
myfun(a,b)
# 3 values(all variables) are passed to the function as arguments
# 3 values(1 variables and 2 literals) are passed to the function as arguments
# Error: missing 1 required positional argument: `z’
Positional arguments are required arguments or
mandatory arguments as no value can be skipped
from function call or you cant change the order of
the argument passing.

K V C o d e r s
2.Default Argument
Default values can be assigned to parameter in function header while defining a function,
these default values will be used if the function call doesn’t have matching arguments as
function definition.
def findresult (mark_secured, passing_mark=30):
if mark_secured>= passing mark:
print(“pass”)
else:
print(“fail”)
findresult(46,40)
findresult(52)
Output:
pass
pass *Note: non-default arguments cannot follow default arguments
Here the argument
passing_mark has assigned
with a default value, the
default value can only be
used if the function call
doesn’t have matching
arguments
for this function call default value will not be used as call have matching arguments, hence
the value 46 is assigned to mark_secured and 40 assigned to passing_mark.
for this function call default value will be used as function call doesn’t have matching
arguments as function definition, hence the value 52 is assigned to mark_secured and the
default value 30 is assigned to passing_mark.

K V C o d e r s
Keyword Argument
Python allows to call a function by passing the in any order, in this case the programmer
have to spcify the names of the arguments in function call.
def findpow(base, exponent):
print(base**exponent)
findpow(5,2)
findpow(exponent=5,base=2)
Output:
25
32
Keyword Arguments
In the 2nd function call base gets the value 2 and
exponent is assigned with the value 5
In the 1st function call base gets the value 5 and
exponent is assigned with the value 2

K V C o d e r s
Variable Length Argument
Variable Length Argument in python permits to pass multiple values to a single parameter.
The variable length argument precedes the symbol ‘*’ in the function header of the
function call.
def findsum(*x):
sum=0
for i in x:
sum=sum+i
print(“sum of numbers is: ’’, sum)
findsum(6,2,8,5,2)
findpow(34,2,4,10,22,14,6)
Output:
sum of numbers is: 23
sum of numbers is: 92
Variable Length Arguments
The function parameter x can hold any number of vaues
passed in function call to this function, here the
parameter x behaves like a tuple.

K V C o d e r s
Returning Values from Function
Functions in python can return back values/variables from the function to the place from
where the function is called using return statement. Function may or may not return values,
python function can also return multiple values.
return statement terminates the function execution if it is encountered.
def sayhello(name):
message=”hello “+ name
return message
m=sayhello(“amit”)
print(m)
Output:
hello amit
Function returns a single value back to the place from
where function was called.

K V C o d e r s
Scope of Variables
Part(s) of the program where the variable is legal and accessible is referred as its scope.
Based on scope, variable are categorized into 2 categories
Local Variable-: Variable defined inside a function is called as Local Variable. Its scope is
limited only within the function in which it is defined.
Global Variable: Variable defined outside all function is called as Global variable.
def findsum(a,b):
c=a+b
return c
x,y=10,20
m=findsum(x,y)
print(m)
Output:
30
Here the variable a, b and c is defined
inside the function, so a, b and c is
Local variables.
The variable x, y and m is are not
defined inside any function, so x, y and
m is Global variables.

K V C o d e r s
Using a Global variable in local scope
To access a variable declared outside all functions(Global Variable) in a local scope then
global statement is used.
When global statement is used for a name, it restrict the function to create a local variable
of that name instead the function uses the global variable.
a=10
def add(x):
a=x+5
print(x)
add(20)
print(a)
Output:
25
10
a=10
def add(x):
global a
a=x+5
print(x)
add(20)
print(a)
Output:
25
25
Inside the function a local variable with name a is
created, so changes to the value of local variable a,
doesn’t affect the value of the global variable a.
Use of the global statement restrict the
function to create a local variable with
name a, instead the function is accessing
the global variable a. So any changes made
to a inside the function will affect the value
of global variable a.

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