This document discusses functions in Python. It defines a function as a named unit of code that can be invoked. Functions help avoid repetitive code by allowing code to be written once and called multiple times. The document covers defining user-defined functions, built-in functions, and functions from modules. It discusses passing arguments to functions, including positional arguments, default arguments, and named arguments. It also covers scope, returning values from functions, and some rules around default arguments and named arguments. Examples are provided to demonstrate defining and calling functions in Python code.

1. Working with Functions
Intro, Understanding & Defining Functions
Parameters, Returning, Scope
Lectures by Harsh Sharma @ Apni Kaksha

2. Functions ( )
In large programs, we try to avoid a single large list of instructions.
It’s broken down into smaller units known as Functions.
A Function is a named unit of a group of program statements. This unit can
be invoked.
A Function is a subprogram/mini-program.
Function ki pehchaan

3. What is a Function?
When we know some things are repetitive or very similar.
To avoid writing same code again and again, we write it once and give it a
name.
This name is the function name, and whenever we call this name the code in
it will run.

4. Types of Functions
1. User Defined Functions : Designed by Programmers, like we will make.
2. Built-in Functions : Functions already present in python.
(pre-defined) e.g. input( ), len( ), int( ), etc.
3. Functions defined in : These are also predefined but in modules.
Modules To use them we have to import the corresponding
module/library.
e.g. factorial( ), sqrt( ), plot( ), etc.

5. Minimizing Repetitions
def greeting( ):
print(“Mere pyaare desh vaasiyon...”)
print(“....”)
print(“Mitrrooonnn!!!”)
greeting( )
Will run the three 3 statements.
#code_minimized.

6. When we have Similar Codes
print(‘Hello Passengers, this train will go to Delhi’)
print(‘Hello Passengers, this train will go to Lucknow’)
print(‘Hello Passengers, this train will go to Mumbai)
print(‘Hello Passengers, this train will go to Chandigarh’)
print(‘Hello Passengers, this train will go to Mars’)
def announcement(a) :
print(‘Hello Passengers, this train will go to’ ,a)
announcement(‘Delhi’)
announcement(‘Lucknow’)
announcement(‘Mumbai’)
announcement(‘Chandigarh’)
announcement(‘Mars’)

7. def sum(x, y) :
print(x+y)
Elements 0f a Function Definition
Function Header
Function Body
Keyword for
defining
parameters/arguments

8. Structure of a Python Program(not imp.)
def function1( ) :
:
def function2( ) :
:
#top level statements
statement1
statement2
:
Interpreter start _main_ se karta hai
Top to Bottom

9. Flow of Execution(learn the flow)
def fun( ) :
print(‘Hello’)
:
print(‘Babye’)
:
fun( )
:
:
Top to Bottom
Interpreter start _main_ se karta hai

10. Practice Time
Q1. w.a.p. to add two numbers using function. (using return)

11. Arguments : values being passed as arguments.
Parameters : values being received as arguments.
def multiply(x,y): parameters
return(x*y)
multiply(3,5) arguments
Arguments & Parameters

12. Arguments can be literals, variables, expressions.
But Parameters have to be some name/identifier, variable to hold incoming
values.
We can also call them :
Argument -> Actual Parameter or Actual Argument
Parameter-> Formal Parameter or Formal Argument
Arguments & Parameters

13. Passing Arguments
def calculate( a ,b ,c ):
:
calculate( 2, 4, 1 )
calculate( x, 8, 3 )
calculate( p, q, r )
calculate( 2, 1)
calculate( 5 )
*Positional arguments or Required arguments or Mandatory Arguments

14. Default Arguments
Sometimes we need passing arguments to be optional, i.e. if an argument is
passed we will use it and if not we will use the default value for that.
e.g. def food( main=‘Tinde’, sec=‘Parle-G’):
: : :
food(‘Paneer’, ‘Pulaao’)
food(‘Pasta’)
food( )

15. Important Rules for Default Parameters
Any parameter cannot have a default value unless all parameters appearing on
its right have default values.
def interest ( prin, time, rate = 0.15 ): ✔
def interest ( prin, time = 3, rate = 0.10 ):✔
def interest ( prin, time = 2, rate ): ❌
interest ( 3000, 5 )
interest ( 3000 )

16. Named Arguments
def interest ( prin, time, rate=0.15 ):
:
interest( rate=0.12, time=8, prin=1000 )
interest( time=5, rate=0.15, prin=2500 )
interest( time=5, prin=2500 )
interest( 1000, rate=0.12, time=4 )
Positional( required ) named

17. Some more rules
interest ( prin, time, rate=0.12 )
● As default parameters, named arguments also follow the rightmost
rule.
interest( prin=2000, 3, 0.15)
● No Multiple Values
interest( 2000, prin=1000,time=3.5 )
● No Parameter can be left empty
interest( prin=2000, rate=0.3 )

18. Practice Time
Q1. Find the output :
def interest( p , t=2, r = 0.10 ):
return (p*t*r)
print( interest(6100, 1) )
print( interest(5000, r = 0.05) )
print( interest(5000, 3, 0.12) )
print( interest(t=4, p=5000) )
Q2. What’s wrong with the code:
def add(a, b, c):
return a+b+c
print( “the answer is : ”, a+b+c )

19. Practice Time
Q. Find the output :
def change(P, Q = 30):
P = P + Q
Q = P - Q
print(P, ‘#’, Q)
return(P)
A = 150
B = 100
A = change( A, B)
print(A, ‘#’, B)
B = change(B)
Q. Find the output :
def fun(s):
k=len(s)
m=‘ ’
for i in range (0,k):
if(s[i].isupper( )):
m = m + s[i].lower( )
elif(s[i].isalpha( )):
m = m + s[i].upper( )
else :
m = m + ‘bb’
print(m)
fun(‘@gmail.com’)