Introduction to Python

Chapter 20 - Repetition Structures in Python

Quick Recap

In previous Chapter, I presented the following main concepts:

Real-world Problem
- Definition
  - A Real-world Problem is defined as a matter or situation regarded as unwelcome or harmful and needing to be deal with and overcome
- Purpose – Why Solve a Real-world Problem?
  - To improve the quality of human life
Programming Problem
- Definition
  - To analyze the program before writing it is known as Programming Problem
- Purpose
  - The main purpose of Programming Problem is to identify the following parameters from the given Program:
    - Identify the input
    - Identify Purpose of Program and Operators performed on a Program
    - Display the Output
Python Control Structures
- In Python Programming, three main Python Control Structures are
  - Sequential Structure
  - Selection Structure
  - Repetition Structure
Sequential Structure
- Definition
  - A Sequence Structure executes a Sequence of Python Statements one by one in the order in which they are written
- Purpose
  - The main purpose of Sequential Structure it to
    - Execute Python Statements one by one in the order
Selection Structure
- Definition
  - A Selection Structure (a.k.a. Conditional Structure) is a feature of Python Programming Language that is used to perform different actions / tasks based on Decision Making (whether a specific Condition is True or False)
- Purpose
  - The main purpose of Selection Structures is
    - Decision Making
Repetition Structure
- Definition
  - A Repetition Structure is a feature of Python Programming Language that is used to perform Repetitive Python Programming Tasks
- Purpose
  - The main purpose of Repetition Structure it to perform Repetitive Programming Task
Decision
- Definition
  - Decision can be defined as an act of Selecting / Choosing one action from several alternatives
Decision-Making
- Definition
  - Decision-Making is defined as the process of making Decision
- Purpose
  - The main purpose of Decision-Making is to
    - Take Most Suitable Actions to Perform Various Real-world Tasks
Decision Making in Python
- Definition
  - In Python Program, Outcome of a Condition (Relational Expression, logical Expressions, Boolean Expressions and Arithematic Expressions) is used to make a Decision (i.e., which Block of Code will be executed)
Conditionals in Python
- Definition
  - A statement that controls the flow of execution depending on some condition
- Purpose
  - The main purpose of Conditional Statements is to perform different operations depending upon the condition
Conditions in Python
- Definition
  - The Boolean Expression is a conditional statement which determines which block will be executed
- Purpose
  - Conditions control the flow of execution of Programs based on conditionals
Relational Operator
- Definition
  - Relational operator is a programming language construct or operator that tests or defines some kind of relation between two entities
If Statement
- Definition
  - if statement is an expression that can be evaluated as True or False and is called a conditional test
  - It executes a set of statements conditionally, based on the value of a logical expression
Purpose
- The main purpose if statement is that it takes the form of an if test, followed by one or more optional elif (“else if”) tests and a final optional else block
  - Python if Statement is used for decision-making operations
Else Statement
- Definition
  - else condition can be optionally used to define an alternate block of statements to be executed if the boolean expression in the if condition evaluates to False
Purpose
- In programming languages, The else keyword is used in conditional statements (if statements), is an alternative statement that is executed if the result of a previous test condition evaluates to false
Elif Statement
- Definition
  - The elif is short for else if. It allows us to check for multiple expressions. If the condition for if is False , it checks the condition of the next elif block and so on. If all the conditions are False , the body of else is executed
- Purpose
  - The main purpose is that the elif condition is used to include multiple conditional expressions after the if condition or between the if and else conditions. The elif block is executed if the specified condition evaluates to True
Nested IF
- Definition
  - if statements inside if statements, this is called nested if statements
- Purpose
  - The main purpose of Nested if statements are often used when you must test a combination of conditions before deciding on the proper action

Real-world Repetitive Task

Definition
- A Real-world Repetitive Task is made up of a set of action(s) that are repeated over and over again (and may involve small variations in each iteration)
Purpose
- The main purpose of a Real-world Repetitive Task is to
  - Break a big Real-world Task into several (very similar) Sub-tasks and repeat a set of actions(s) over and over again on Sub-tasks to complete the big Real-world Task
Importance
- In any field of life, you cannot become an Authority in that field, unless and until you Repeat (Practice) the same set of Real-world Tasks under the supervision of a Guru (i.e., a Teacher, who is an Authority in that field)
Remember the famous quote 😉
- Practice enables a Man to achieve Excellence in any Real-world Task
Advice of My Respected Teacher
- Adeel! Always put 100% Effort with Sincerity to Achieve PERFECTION in your field (i.e., in any Real-world Task your Role Model MUST BE Our Beloved Prophet Hazrat Muhammad S.A.W.W. (حضرت محمد صلی اللہ علیہ وسلم) and Sahaba Karam R.A. (صحابہ کرام رضی اللہ عنہ). However, you will never achieve PERFECTION, but you will achieve EXCELLENCE. Also, when you put 100% Effort into Sincerity then do not bother about the RESULTS (OUTCOMES). Sometimes you will get your desired RESULTS and sometimes you will not get your desired RESULTS. Just keep putting 100% Effort with Sincerity till Death 😊
- To become an Authority in your field, never ever compromise on Character.
- The 3 Main Pillars of Character which we learn from the pious lives of Our Beloved Prophet Hazrat Muhammad S.A.W.W. (حضرت محمد صلی اللہ علیہ وسلم) and Sahaba Karam R.A. (صحابہ کرام رضی اللہ عنہ) are:
  - Truth
  - Honesty
  - Justice
- May Allah give us the taufeeq (توفیق) to become a Man of Character and safeguard our Character till Death. Ameen
Applications
- To perform any Real-world Task with the highest level of quality, you need to
  - Practice it (i.e., REPEAT the same set of action(s) repeatedly)
Strengths
- Using the phenomenon of REPETITION, you can achieve Excellence in any Real-world Task
  - Challenges
    - REPEATING the same set of action(s) is a very tough Task and majority of people in this world fail to do this
Question
- How to overcome the problem of not being able to REPEAT the same set of actions(s) repeatedly?
Answer
- To perform the same set of action(s) REPEATEDLY to Become an Authority in any field of life, you need to follow a Two-Step Process till Death
  - Step 01: Have a Guru (Mentor) in Life
  - Step 02: Report your Daily Work Progress on your Real-world Tasks to your Guru on DAILY BASIS
Motivational Seminar – Guru ke Har Baat Gur Hoti Hai. Gur Ko Nhe Guru Ko Pakar (گرو کے ہر بات گر ہوتی ہے۔ گر کو نہیں گرو کو پکڑ)
- Download Link:
Suitable to Use
- To learn any Real-world Task, we should use the phenomenon of REPETITION 😊

Some of the Real-world Repetitive Tasks (to become an authority in your field), which we learned from the lives of Our Beloved Prophet Hazrat Muhammad S.A.W.W. and Sahaba Karam R.A. are:
- Task 01: Go to bed immediately after Namaz.e.Isha
- Task 02: Start performing your Real-world Tasks after Namaz.e.Fajr
  - Hazrat Muhammad S.A.W.W. said to the nearest meaning
- Task 03: Take Three Healthy Meals on Daily Basis (for e.g., 1 Liter Milk, at least 10 Dates and 5 – 10 Spoons of Honey)
  - My Respected Teacher said
- Task 04: At least 30 Mins Brisk Walk / Running / Game (with Family) on Daily Basis
  - My Respected Teacher said
  - My Respected Teacher said
    - If you Practice Real-world Repetitive Task 01, Real-world Repetitive Task 02, Real-world Repetitive Task 03 and Real-world Repetitive Task 04 then you can Achieve Excellence in Physical Health In Sha Allah
- Task 05: Be Happy, Keep Happy
  - My Respected Teacher said
    - If you Practice this Real-world Repetitive Task, then you can Achieve Excellence in Mental Health In Sha Allah
- Task 06: Do one good deed with any Creature of Allah (to please Allah) on Daily Basis
  - My Respected Teacher said
    - If you Practice this Real-world Repetitive Task, then you can Achieve Excellence in Social Health In Sha Allah
- Task 07: Offer 5 Namaz (نماز) in Masjid (مسجد) with Takbeer.e.Owla (تکبیر اولی) on Daily Basis
- Task 08: Recite Durood Sharif (درود شریف) for at least 30 minutes on Daily Basis
- Task 09: Do Dua (دعا) for at least 5 minutes on Daily Basis
- Task 10: Fast in the Month of Holy Ramazan
- Task 11: Give Sadqa (صدقہ) on Daily Basis
- Task 12: Give Zakat (زکوۃ) (if Zakat is obligatory on you)
- Task 13: Perform Hajj (حج) (if Hajj is obligatory for you)
  - My Respected Teacher said
    - If you Practice the Real-world Repetitive Task from 07 to 13, then you can Achieve Excellence in Spiritual Health In Sha Allah
- Task 14: Love, Respect and Serve Humanity to please Allah
  - My Respected Teacher said

Definition
- Iteration is defined as the repetition of a set of action(s) to produce an Outcome (or Result).
Note
- In one Iteration, the entire set of action(s) is
  - executed only once
- The Outcome (Result) of each Iteration is the Starting Point for the next Iteration
- The Sequence of Iterations will approach the Outcome (Result)

The Two Main Types of Real-world Repetitive Tasks are
- Real-world Repetitive Tasks with Fixed Number of Iterations
- Real-world Repetitive Tasks with Variable Number of Iterations

Real-world Repetitive Tasks with Fixed Number of Iterations

Definition
- Real-world Repetitive Tasks with Fixed Number of Iterations are those Real-world Tasks in which the Number of Iterations needed to complete a Real-world Task are known before we start executing that Real-world Task
Examples
- Some of the Real-world Repetitive Tasks with Fixed Number of Iterations are as follows
  - Fasting in the Holy Month of Ramazan
  - Calculating Average Marks of Class in Python Course
  - Writing the following Text 10 times on a page
    - Allah is One and He has control over everything. Hazrat Muhammad S.A.W.W. is the last Prophet of Allah is the Role Model for us in all walks of life. Alhamdulillah 😊

Real-world Repetitive Tasks with Variable Number of Iterations

Definition
- Real-world Repetitive Tasks with Variable Number of Iterations in which the Number of Iterations needed to complete a Real-world Task are not known before we start executing that Real-world Task
Examples
- Some of the Real-world Repetitive Tasks with a Variable Number of Iterations are as follows
  - Number of Times you Recite Durood Sharif (درود شریف) (in 30 minutes) every day
  - Number of Glasses of water you drink everyday
  - Number of friends you meet (or talk to) everyday

Solving Real-world Repetitive Tasks using Programming Languages

Our Life comprises three main Structures i.e.,
- Sequential Structure
- Selection Structure
- Repetition Structure
One day we were born, and a day will come when we die i.e., a Sequential Structure from Birth to Death 😊
During this Journey from Birth to Death (Sequential Structure), we take various Very Important Decisions (i.e., Selection Structure) and these Decisions force us to repeat certain Real-world Tasks (i.e., Repetition Structure)
For example, if you take the Decision to do BS(CS) from COMSATS University, Lahore then you will have to Repeatedly attend University for the next 4 years of your life 😊
My Respected Teacher advised me
- Adeel! Always Remember that
  - دنیا امتحان کی جگہ ہے اطمینان کی جگہ نہیں ہے
On the Day of Judgment, we will have to answer about all the deeds (good or bad) to Allah and based on our performance in this world we will either enter Paradise or Hell.
The only Goal of our Lives is to
- Achieve Excellence in Friendship of Allah
Therefore, in this Journey from Birth to Death (Sequential Structure), whenever you take a Decision (Selection Structure) and Repeat a Real-world Task (Repetition Structure) based on your Decision, always check
Whether you are getting close to Allah OR far from Allah?
- Always Perform those Real-world Tasks which take you Close to Allah and Never Ever Perform those Real-world Tasks which take you far away from Allah
- May Allah bless all of us with His highest level of Friendship Ameen 😊

Question
- How can we solve Real-world Repetitive Tasks using Programming Languages?
Answer
- Use Repetition Structures of Programming Languages

Since Python Programming Language aims to solve Real-world Tasks using Programming Control Structures, therefore, similar to Control Structures of Life, the three main Python Control Structures are
- Sequential Structure
- Selection Structure
- Repetition Structure

Definition
- A Sequence Structure executes a Sequence of Python Statements one by one in the Order in which they are written
Purpose
- The main purpose of Sequential Structure it to
  - Execute Python Statements one by one in the Order in which they are written
Programming Languages based on Sequential Structures
- Some of the popular and widely used Programming Languages which execute Programs using Sequential Structure are
  - Java
  - C
  - C++
  - Python
  - FORTRAN
  - Basic
  - PL1
  - Pascal

Definition
- A Selection Structure (a.k.a. Conditional Structure) is a feature of Python Programming Language that is used to perform different actions / tasks based on whether a specific Condition is True or False
Purpose
- The main purpose of Selection Structures is
  - Decision Making and
  - Branching i.e., Choosing between two or more alternative paths
Examples of Selection Structures in Python
- Selection Structures used in Python Programming Language are
  - if
  - elif
  - else
Note
- For details on Selection Structures
  - See Chapter 14 – Decision Making Statements in Python

Repetitive Programming Task

A Repetitive Programming Task is defined as a Programming Task in which there is little variation from one item to the next item of the Programming Task

The Two Main Types of Repetitive Programming Tasks are
- Repetitive Programming Task with Fixed Number of Iterations
- Repetitive Programming Task with Variable Number of Iterations

Repetitive Programming Task with Fixed Number of Iterations

Definition
- Repetitive Programming Task with Fixed Number of Iterations are those Repetitive Programming Tasks in which the Number of Iterations is known at the Code Time
Examples
- Some of the Repetitive Programming Tasks with Fixed Number of Iterations are as follows
- Example 01
  - Programming Task 01
    - Display the following Message 5 times on the Output Screen
      - Number of Iterations
        5 (i.e., Fixed)
- Example 02
  - Programming Task 02
    - Display Names of 30 Students enrolled in Python Course
      - Number of Iterations
        30 (i.e., Fixed)
- Example 03
  - Programming Task 03
    - Display all Even Numbers in the Range 51 – 100
      - Number of Iterations
        50 (i.e., Fixed)
- Example 04
  - Programming Task 04
    - Display Average Marks of 100 Students enrolled in Python Course
      - Number of Iterations
        100 (i.e., Fixed)
- Example 05
  - Programming Task 05
    - Print the Table of 2 on the Output Screen
      - Number of Iterations
        10 (i.e., Fixed)

For majority of Repetitive Programming Tasks, the Number of Iterations is
- Fixed

Repetitive Programming Task with Variable Number of Iterations

Definition
- Repetitive Programming Task with Variable Number of Iterations are those Repetitive Programming Tasks in which the Number of Iterations are not known at the Code Time
Examples
- Some of the Repetitive Programming Tasks with Variable Number of Iterations are as follows
  - Example 01
    - Programming Task 01
      - Ms. Samavi running a Python Program (called addition.py) to strengthen and practice basic addition concepts of Math. The addition.py Program works as follows: (1) Takes Two Integer Numbers as Input (from User) and displays their Sum on the Output Screen, and (2) Asks Ms. Samavi whether she wants to calculate Sum of Two Integer Number again or quit?
    - Number of Iterations
      - Variable
  - Reason for Variable Number of Iterations
    - In above Programming Task, the Number of Iterations will be Variable each time Ms. Samavi runs addition.py Python Program because
      - We don’t know, how many times (Iterations) Ms. Samavi would like to calculate Sum of Two Integer Numbers?

Menu – in Programming

Definition
- In Programming, a Menu is defined as a List of Options (Choices)
Example – Menu in Programming
- Consider the following Menu for a Library System developed using Python Programming Language
  - Enter a to Add a New Book
  - Enter d to Delete an Existing Book
  - Enter u to Update an Existing Book
  - Enter s to Search a Book
  - Enter e to Exit
  - Please Enter Your Choice:

Definition
- A Menu Driven Program is a Program which takes Input from a User by displaying a Menu (i.e., a List of Options (Choices)) and the User indicates his / her Choice form the given Menu
Examples – Menu Driven Programs
- Some of the popular and widely used Examples of Menu Driven Program are as follows
  - ATM Machine
  - Online Shopping Websites
  - Microwave Oven
  - Washing Machine
  - iPod or Mobile Phone
  - And Many More 😊

For majority of Menu Driven Repetitive Programming Tasks, the Number of Iterations is
- Variable

Chapter Summary

In this Chapter, I presented the following main concepts:

Real-world Repetitive Task
- Definition
  - A Real-world Repetitive Task is made up of a set of action(s) that are repeated over and over again (and may involve small variations in each iteration)
- Purpose
  - The main purpose of a Real-world Repetitive Task is to
    - Break a big Real-world Task into several (very similar) Sub-tasks and repeat a set of actions(s) over and over again on Sub-tasks to complete the big Real-world Task
Iteration
- Definition
  - Iteration is defined as the repetition of a set of action(s) to produce an Outcome (or Result).
Types of Real-world Repetitive Tasks
- The Two Main Types of Real-world Repetitive Tasks are
  - Real-world Repetitive Tasks with Fixed Number of Iterations
  - Real-world Repetitive Tasks with Variable Number of Iterations
Repetitive Programming Task
- A Repetitive Programming Task is defined as a Programming Task in which there is little variation from one item to the next item of the Programming Task
Types of Repetitive Programming Task
- The Two Main Types of Repetitive Programming Tasks are
  - Repetitive Programming Task with Fixed Number of Iterations
  - Repetitive Programming Task with Variable Number of Iterations
Menu Driven Program
- Definition
  - A Menu Driven Program is a Program which takes Input from a User by displaying a Menu (i.e., a List of Options (Choices)) and the User indicates his / her Choice form the given Menu
Repetition Structure
- Definition
  - A Repetition Structure (a.k.a. Loop) is a feature of Python Programming Language that is used to perform Repetitive Python Programming Tasks
- Purpose
  - The main purpose of Repetition Structure it to perform Repetitive Programming Tasks
Four Main Components of a Loop (Repetition Structure)
- In Python Programming, the Four Main Components of a Loop are
  - Initialization
  - Condition (Test)
  - Body of Loop
  - Increment / Decrement
while Loop
- Definition
- In Python Programming, a while loop is used to execute a Set of Python Statements (i.e., Perform a Repetitive Programming Task) if a Condition is True
Purpose
- The main purpose of while Loop is to
  - Perform Repetitive Programming Tasks
for Loops
- Definition
  - The for loop in Python is used to iterate the statements or a part of the program several times
- Purpose
  - The for loop is a generic sequence iterator in Python: it can step through the items in any ordered sequence objects

Ilm o Irfan

Introduction to Python

Table of Contents

Chapter 20 - Repetition Structures in Python

Quick Recap

Real-world Repetitive Task

Real-world Repetitive Tasks with Fixed Number of Iterations

Real-world Repetitive Tasks with Variable Number of Iterations

Solving Real-world Repetitive Tasks using Programming Languages

Repetitive Programming Task

Repetitive Programming Task with Fixed Number of Iterations

Repetitive Programming Task with Variable Number of Iterations

Menu – in Programming

Chapter Summary

In Next Chapter

Chapter 19 - Nested Selection Structures

Chapter 21 - while Repetition Structure

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