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Topic 1: Pre-defined and User-defined Functions

Learning outcomes:�

(c) Identify the components of a function:�

Function Header
Function Body
Function Call

(1 hour)

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Table of Contents (TOC)

Introduction to Namespace
Three components of a function

i. Function Header

ii. Function Body

iii. Function Call

Example Function Call
How the program execute when the function is called
Function Call without argument(s)
Function Call with argument(s)
Parameter vs argument

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Introduction to Namespace

## Function space ##

def hi():

print("hi!")

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Global space refers to the namespace that is outside of the function space.
In this course we use the term global space and main space interchangeably.
Moving forward, the main space is the term that we will use.

## Main space ##

hi()

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i. Function Header

ii. Function Body

(indented)

Three components of a function:

i. Function Header

ii. Function Body

iii. Function Call

def greet ( ) :

print (“Hello World!”)

greet( )

iii. Function Call/ invoke

Function Definition

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https://wayground.com/join/quiz/6933f1a86ec2d3942ead0fb9?studentShare=true

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Four Elements in Function Header

def keyword is used at the start of function header

(2) Function name �(define by user or built in function)

(4) colon (:) at the end of function header

def greet ( ) :

(3) parentheses ( ) with and without parameter/ input values

i. Function Header

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Examples of Function Header

Function header without parameter

Function header with parameter

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The function header name is using snake_case naming convention
Parameter - Input value(s) for the function to process.
Example - no1, no2 and no3 that will be processed to find the average

def find_total(a, b):

def display_lect(name):

def find_avg(no1, no2, no3):

def status():

def message():

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Exercise 1�

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Exercise 1.1 �

(i) Create a function header named determine_grade without parameter.

def _________ _

(ii) Create a function header named display_message without parameter.

_______ _______ () :

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Exercise 1.1 �

(iii) Create a function header named calc_total that accepts two parameters, a and b.

_______ total(___, b):

(iv) Create a function header named calc_sum that accepts two parameters named num1 and num2.

___ ________ (______, ________) :

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(i) This function named display_msg() is to display “Welcome back”. Identify the errors from this snippet below.

Exercise 1.2

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## create function ##

def display_msg();

print("Welcome back")

## main ##

msg()

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(i) This function named display_msg() is to display “Welcome back”. Identify the errors from this snippet below.

Exercise 1.2

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(ii) This function named display_msg() is to display “Welcome back”. Identify the error from this snippet below.

Exercise 1.2

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## create function ##

def display_msg():

print("Welcome back")

## main ##

display_msg()

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(iii) This function named display_msg() is to display “Welcome back”. Identify the error from this snippet below.

Exercise 1.2

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## create function ##

def display_msg:

print("Welcome back")

## main ##

display_msg()

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(iv) This function named display_msg() is to display “Welcome back”. Identify the error from this snippet below.

Exercise 1.2

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## create function ##

defdisplay_msg():

print("Welcome back")

## main ##

display_msg()

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ii. Function Body

The body of function consists of one or more valid statements.(Eg: to calculate max, to print value)

Each statement must be indented with the same indentation to form a block.

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ii) Function Body (without or with return values)

Function body without return value

(no return keyword)

Function body with return value �(must have return keyword)

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Example of Function Body

Function body without

return value (no return keyword)

(b) Function body with

return value (must have return keyword)

Function body

Function body with return keyword

Function body

Function body with return keyword

def calcAvg(num1,num2,num3):

total = num1 + num2 + num3

avg = total/3

return avg

def greet(message):

return message

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iii) A. Function Call

Function without function call is meaningless.

Therefore, we need to create function call.

To call a function, use the function name followed by parenthesis(), with or without arguments.

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iii) A. Function Call - continued

Once the function is invoked (called) in main program space, the parameters inside the parentheses () is called arguments.
The number of arguments must match with parameters of the function.
Arguments must have values

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Arguments

Parameters

Function call

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Example Function Call Without Arguments

function call (name must be the same as function name)

function header

function body

function space

main program space

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When the function greet() is called from the main space, the program's control transfers to the function definition in function space.
All the code inside the function is executed.

iii) B. How the program execute when the function is called

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iii) C. Function Call without argument(s)

Function call without argument(s)

1.1 Without return value

1.2 With return value

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Return value is the result that a function sends back to the main space after it finishes running.

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Function Call without argument(s)

function call

1.1 Without return value

Output:

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Function Call without argument(s)

1.2 With return value

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## create function ##

def get_greeting():

return "Hello, welcome back!"

## main ##

print(get_greeting())

## create function ##

def get_greeting():

return "Hello, welcome back!"

## main ##

message = get_greeting()

print(message)

Output:

*Direct print from the returned value

*Store returned value in a variable to be used later

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iii) D. Function Call with argument(s)

Function call with argument(s)

1.1 Without return value

1.2 With return value

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iii) D. Function Call with argument(s)

2.1 Without return value

2.2 With return value

function call with argument

Output:

function call

with arguments

Output:

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Parameter vs Argument

Parameter: in function header (function space)
Argument: in function call (main program space)�

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Recap

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parameters�(variable)

2, 3

4, 20

length, width

arguments

(values)

Output:

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parameters used in function header

arguments used in function call

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Output:

we could assign function call to a variable

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Exercise 1�

Write a function to calculate area of a rectangle (with and without return value)

length = float(input("Enter the length of the rectangle: "))

width = float(input("Enter the width of the rectangle: "))

area = length * width

print("The area of the rectangle is:", area)

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Exercise 2�

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(i) Create a function header named bmi()that accepts two

parameters named height and weight.

(ii) Call the previous function by using the values 1.53 and

55 for height and weight respectively. (Assume there is

a return values)

Exercise 2.1

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(i) Create a function header named sum()that accepts

three integers value named num1, num2 and num3.

(ii) Call the previous function by using the values 10, 20

and 30 for num1, num2, and num3 respectively.

(Assume there is a return values)

(iii) Identify the arguments and parameters from (i) and (ii)

Exercise 2.2

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Summary

Introduction to Namespace
Three components of a function

i. Function Header

ii. Function Body

iii. Function Call

Example Function Call
How the program execute when the function is called
Function Call without argument(s)
Function Call with argument(s)
Parameter vs argument

CP125