Python Programming Notes

Python Programming Notes - 9

Part – 1 : Programming Concept

1. Program

A Program is a set of instructions written in a high-level programming language to perform a specific task or solve a particular problem. The computer executes these instructions one by one to produce the desired output.

Example: A program to calculate the simple interest, display the multiplication table of a number, or find the largest among three numbers.

2. Program Development Life Cycle (PDLC)

The Program Development Life Cycle (PDLC) is a systematic process followed while developing a computer program. It helps programmers create efficient, reliable, and error-free programs.

3. Algorithm

An Algorithm is a step-by-step procedure or set of instructions used to solve a problem or perform a specific task. Algorithms are written in simple language and are independent of any programming language.

Characteristics of an Algorithm:

Easy to understand.
Consists of finite steps.
Produces the desired output.
Helps in planning a program before coding.

4. Flowchart

A Flowchart is the graphical representation of an algorithm using different standard symbols connected with arrows to show the sequence of execution.

Flowcharts make it easier to understand the logic of a program before writing the actual code.

Practice Algorithms and Flowcharts

Create algorithms and flowcharts for the following problems:

To prepare tea.
To add two numbers.
To find the product of three numbers.
To calculate the simple interest.

Note: The above questions are based on a Sequential Program Flow.

5. Program Flow

Program Flow is the direction in which a program executes. It describes how the statements of a program are executed and determines the possible outcomes of the program.

There are three types of program flow structures in programming:

Sequential Flow
Conditional Flow
Iterative (Looping) Flow

1. Sequential Flow

Sequential Flow is the simplest program flow in which statements are executed one after another in the order they appear. There is only one starting point and one ending point without any decision-making or repetition.

Structure:

One Start
Sequential execution of statements
One End

    Start
      ↓
    Step 1
      ↓
    Step 2
      ↓
    Step 3
      ↓
    Stop

2. Conditional Flow

Conditional Flow is a program flow in which a condition is checked before deciding which path the program should follow. Depending on whether the condition is true or false, different statements are executed.

Structure:

One Start
Sequential execution
One Decision Box
Multiple possible results

Condition Checking:

    Step X: Is condition?
          Yes → Result 1
          No  → Result 2

Note: The keyword goto can be used to point the program flow directly to a particular step. It is better understood while studying looping.

3. Iterative (Looping) Flow

Iterative Flow, also known as Looping, is a program flow in which a set of statements is repeated as long as a certain condition remains true. When the condition becomes false, the loop ends and the program continues with the next statement.

Structure:

    Step X: Is condition?
          Yes → Go to Step Y
          No  → Go to Step Z
    Step Y: Perform Calculation, Go to Step X
    Step Z: Stop

Looping is mainly used when the same task needs to be performed repeatedly without writing the same statements multiple times.

Practice Algorithms and Flowcharts

Sequential

To add two numbers.
To find the simple interest when principle, time and rate is given by the user.
To find the area of rectangle.
To find the volume of cylinder.

Conditional

To check if a person is eligible to vote or not.
To find the greater of two numbers.
To find the smallest of three numbers.
To check if a number is even or odd.
To check if a number is positive, negative or zero.

Looping

To display your name 10 times.
To display the table of 3 upto the 10th multiple.
To display even numbers upto 200.
To display odd numbers from 100 to 200.

Basic Terminologies

1. Programming Language

A programming language is a formal language used to write instructions that a computer can understand and execute to perform a specific task.

Examples: Python, C, C++, Java, JavaScript, etc.

2. Programmer

A programmer is a person who writes, tests, debugs, and maintains computer programs using one or more programming languages.

3. Programming

Programming is the process of designing, writing, testing, debugging, and maintaining a computer program using a programming language.

4. Syntax

Syntax refers to the set of rules that determine how statements and instructions must be written in a programming language. If these rules are not followed, a syntax error may occur.

Example in Python:

print("Hello World")

Types of Programming Languages

Programming languages can be broadly classified into the following types:

1. Machine Language

Machine language is the lowest-level programming language that consists of binary digits (0 and 1) and can be directly understood and executed by the computer.

Example:

10110000 01100001

2. Assembly Language

Assembly language is a low-level programming language that uses symbolic instructions or mnemonics instead of binary numbers. It requires an assembler to convert the instructions into machine language.

Examples of mnemonics:

3. High-Level Language

A high-level language is a programming language that uses English-like words and mathematical symbols, making it easier for humans to read, write, and understand. It requires a compiler or interpreter to translate the program into machine-understandable instructions.

Examples: Python, C, C++, Java, BASIC, etc.

Advantages of Writing an Algorithm

Provides a clear solution.
Makes programming easier.
Makes debugging easier.

Advantages of Designing a Flowchart

Easy to understand.
Helps in identifying errors.
Helps in program development.

Coding

Coding is the process of converting an algorithm or program design into instructions using a particular programming language.

For example, writing a Python program based on an algorithm is called coding.

Testing

Testing is the process of executing a program with different inputs to check whether it produces the expected output and works correctly.

Types of Testing

Software testing can be broadly classified into Black Box Testing and White Box Testing.

1. Black Box Testing

Black box testing is a type of testing in which the tester checks the functionality and output of a program without knowing or examining its internal source code or implementation.

The tester mainly focuses on inputs and expected outputs.

Example:

A tester enters different usernames and passwords into a login system and checks whether the correct result is produced.

2. White Box Testing

White box testing is a type of testing in which the tester examines the internal structure, logic, and source code of a program while testing it.

The tester checks whether the different statements, conditions, loops, and paths of the program work correctly.

Example:

A programmer examines whether every condition in an if-else statement and every iteration of a loop works correctly.

Debugging

Debugging is the process of identifying, locating, and correcting errors or bugs in a computer program.

Example: If a program produces an incorrect result because of an incorrect calculation, finding and correcting that mistake is debugging.

Difference Between Compiler and Interpreter

Compiler	Interpreter
A compiler translates the entire source program into machine code before execution.	An interpreter translates and executes the source program one statement at a time.
A compiler generally reports errors after analyzing the source program during compilation.	An interpreter generally reports an error when it reaches the statement containing the error during execution.
A compiled program generally executes faster because the translation has already been completed before execution.	An interpreted program generally executes more slowly because translation takes place during execution.

Part – 2 : Python Basics

Python

Python is a high-level, interpreted, general-purpose programming language used to develop software, websites, applications, automation scripts, data analysis programs, artificial intelligence systems, and many other types of software.

Python was designed by Guido van Rossum and was first released in 1991.

Key Features of Python

Python has a simple and easy-to-understand syntax.
It is an interpreted programming language.
It supports object-oriented programming.
It is a high-level programming language.
Python is case-sensitive.

Advantages of Python

Easy to Learn
Free and Open Source
Cross-Platform
Large Library Support

Variable

A variable is a name given to a memory location that is used to store a value in a program.

In Python, a variable is created when a value is assigned to it using the assignment operator (=).

Syntax

variable_name = value

Examples

name = "Tejas"
age = 25
marks = 85.5

Python does not require the programmer to declare the data type of a variable explicitly.

Rules for Naming Variables in Python

The following rules should be followed when naming a variable:

A variable name must begin with a letter or an underscore (_).
A variable name cannot begin with a number.
A variable name can contain letters, digits, and underscores.
Spaces are not allowed in variable names.
Python variable names are case-sensitive.
Python keywords cannot be used as variable names.
Example:
```
if = 10     # Invalid
```
Variable names should be meaningful and descriptive.
Special symbols such as @, #, $, %, etc. cannot be used in variable names.

Operators

An operator is a symbol or special keyword used to perform an operation on one or more values or variables.

The values or variables on which an operator works are called operands.

Example

a + b

Here, + is the operator, while a and b are operands.

Types of Operators in Python

The major types of operators in Python are:

Arithmetic Operators
Relational Operators
Assignment Operators
Logical Operators

1. Arithmetic Operators

Arithmetic operators are used to perform mathematical calculations.

Operator	Meaning	Example	Result
+	Addition	10 + 3	13
-	Subtraction	10 - 3	7
*	Multiplication	10 * 3	30
/	Division	10 / 3	3.333...
//	Integer Division	10 // 3	3
%	Modulus	10 % 3	1
**	Exponentiation	10 ** 3	1000

2. Relational/Comparison Operators

Comparison operators are used to compare two values. They return either True or False.

Operator	Meaning	Example
==	Equal to	5 == 5
!=	Not equal to	5 != 3
>	Greater than	5 > 3
<	Less than	3 < 5
>=	Greater than or equal to	5 >= 5
<=	Less than or equal to	3 <= 5

3. Assignment Operators

Assignment operators are used to assign or update values in variables.

Operator	Meaning	Example
=	Assign	x = 10
+=	Add and assign	x += 5
-=	Subtract and assign	x -= 5
*=	Multiply and assign	x *= 5
/=	Divide and assign	x /= 5
//=	Floor divide and assign	x //= 5
%=	Modulus and assign	x %= 5
**=	Exponentiate and assign	x **= 2

4. Logical Operators

Logical operators are used to combine or reverse conditions.

Operator	Meaning
and	Returns True if both conditions are true
or	Returns True if at least one condition is true
not	Reverses the result of a condition

Basic Data Types in Python

A data type specifies the type of value stored or represented in a program. Python provides several built-in data types.

The basic data types commonly used in Python are:

Integer (int)
Floating Point (float)
Boolean (bool)
String (str)

1. Integer (int)

The int data type is used to store whole numbers without decimal points.

Example

age = 20

Integers can be positive, negative, or zero.

2. Floating Point (float)

The float data type is used to store numbers containing decimal points.

Example

price = 99.50

3. Boolean (bool)

The Boolean data type represents one of two possible values:

True
False

Boolean values are commonly used in conditions and decision-making.

Example

age = 20
print(age >= 18)

Output

True

4. String (str)

A string is a sequence of characters enclosed within single quotes, double quotes, or triple quotes.

Strings can contain letters, numbers, spaces, and special characters.

Example

course = "Python Programming"

Python Sequential Programs

  #sum of 2 numbers
  a=int(input("Enter first number:"))
  b=int(input("Enter second number:"))
  s=a+b
  print(f"The sum of {a} and {b} is {s}.")

  #Simple interest
  p=int(input("Enter Principle:"))
  t=int(input("Enter Time:"))
  r=int(input("Enter Rate:"))
  si=(p*t*r)/100
  print("Simple Interest:",si)

  #Area of Circle
  r=int(input("Enter radius:"))
  area=(22/7)*r**2
  print("Area:",area)

  #Volume of cylinder
  r=int(input("Enter radius:"))
  h=int(input("Enter height:"))
  volume=(22/7)*(r**2)*h
  print(f"Volume: {volume}")

  #Temperature Conversion
  c=float(input("Enter celsius:"))
  f=(9/5)*c+32
  print(f"Conversion of {c}C: {f}F.")

  #Time Conversion
  mins=int(input("Enter minutes:"))
  hrs=mins//60
  minutes=mins%60
  print(f"{mins} mins : {hrs} hrs and {minutes} mins.")

  #Time Conversion - 2
  days=int(input("Enter days:"))
  yrs=days//365
  rem_days=days%365
  months=rem_days//30
  final_days=rem_days%30
  print(f"{days}days : {yrs} yrs {months} months {final_days} days.")

Part – 3 : Conditional Programming

Introduction

In Python programming, sometimes we need to make a decision based on a condition.

For example:

If a student scores 40 or more marks, the student passes.
If a person's age is 18 or more, the person can vote.
If a number is divisible by 2, it is even.

To make such decisions, Python provides conditional statements.

Definition

A conditional statement is a statement that allows a program to make decisions and execute different instructions depending on whether a condition is True or False.

What is a Condition?

A condition is an expression that produces either:

True
False

Example:


    age = 18

    print(age >= 18)

Output:

True

Types of Conditional Statements

Python mainly provides the following conditional statements:

if statement
if-else statement
if-elif-else statement
Nested if statement

The if Statement

The if statement executes a block of code only when a condition is True.

Syntax:


    if condition:
        statement

Notice the colon (:) after the condition.

Example:


    age = 20
    if age >= 18:
        print("You are eligible to vote.")

Output:

You are eligible to vote.

If the condition is false, the statement inside the if block is not executed.

Indentation in Python

Python uses indentation to identify a block of code.


    age = 20
    if age >= 18:
        print("Adult")

The print() statement is indented, so Python knows that it belongs to the if statement.

Incorrect:


    age = 20
    if age >= 18:
    print("Adult")

This produces an indentation error.

Remember

After a conditional statement, use:

A colon (:)
Proper indentation

The if-else Statement

The if-else statement is used when there are two possible outcomes.

Syntax:


    if condition:
        statement1
    else:
        statement2

If the condition is True, the if block executes.

If the condition is False, the else block executes.

Example:


    marks = 65
    if marks >= 40:
        print("Pass")
    else:
        print("Fail")

Output:

Pass

Another Example:


    number = 7
    if number % 2 == 0:
        print("Even")
    else:
        print("Odd")

Output:

Odd

Here, % is the modulus operator, which gives the remainder.

The if-elif-else Statement

Sometimes a program needs to check more than two conditions. In such cases, we use if-elif-else.

Syntax:


    if condition1:
        statement1
    elif condition2:
        statement2
    elif condition3:
        statement3
    else:
        statement4

Python checks the conditions from top to bottom.

The first condition that is True is executed.

Example: Grade System


    marks = 75
    if marks >= 80:
        print("Grade A")
    elif marks >= 60:
        print("Grade B")
    elif marks >= 40:
        print("Grade C")
    else:
        print("Fail")

Output:

Grade B

How it works

For marks = 75:

75 >= 80 → False
75 >= 60 → True
Therefore, "Grade B" is printed.
Python does not check the remaining conditions.

The else Statement

The else block is executed when none of the previous conditions are true.

Example:


    temperature = 15
    if temperature > 30:
        print("Hot")
    elif temperature >= 20:
        print("Warm")
    else:
        print("Cold")

Output:

Cold

The else statement does not have a condition.

Nested if Statement

An if statement placed inside another if statement is called a nested if statement.

Example:

age = 20
    citizen = True

    if age >= 18:
        if citizen:
            print("Eligible to vote")

Output:

Eligible to vote

The inner if is checked only when the outer if condition is true.

Example: Check Positive or Negative


    number = int(input("Enter a number: "))
    if number >= 0:
        print("Positive")
    else:
        print("Negative")

Example Output:

Enter a number: -5
    Negative

Example: Find the Greater Number


    a = int(input("Enter first number: "))
    b = int(input("Enter second number: "))
    if a > b:
        print("First number is greater")
    elif b > a:
        print("Second number is greater")
    else:
        print("Both numbers are equal")

Example: Check Voting Eligibility


    age = int(input("Enter your age: "))
    if age >= 18:
        print("Eligible to vote")
    else:
        print("Not eligible to vote")

Example: Simple Calculator Using Conditions


    a = int(input("Enter first number: "))
    b = int(input("Enter second number: "))
    operator = input("Enter operator (+ or -): ")
    if operator == "+":
        print(a + b)
    elif operator == "-":
        print(a - b)
    else:
        print("Invalid operator")

Common Mistakes

Mistake 1: Using = instead of ==

Incorrect:


    if age = 18:
        print("Adult")

Correct:


    if age == 18:
        print("Adult")

Mistake 2: Forgetting the colon

Incorrect:


    if marks >= 40
        print("Pass")

Correct:


    if marks >= 40:
        print("Pass")

Mistake 3: Incorrect indentation

Incorrect:


    if age >= 18:
    print("Adult")

Correct:


    if age >= 18:
        print("Adult")

C. Programming Exercises

Write a program to check whether a number is positive or negative.

n=int(input("Enter a number:"))
if(n>0):
	print("The number is Positive.")
elif (n<0):
	print("The number is Negative.")

Write a program to check whether a number is even or odd.

n=int(input("Enter any number:"))
if (n%2==0):
	print(f"{n} is an even number.")
else:
	print(f"{n} is an odd number.")

Write a program to check whether a student has passed or failed. Consider 40 as the passing mark.

marks=int(input("Enter your marks:"))
if marks>=40:
	print("You have passed.")
else:
	print("You have failed.")

Write a program to find the greater of two numbers.

a=int(input("Enter first number:"))
b=int(input("Enter second number:"))
if a>b:
	print(a,"is greatest.")
else:
	print(b,"is greatest.")

Write a program to check whether a person is eligible to vote.

age=int(input("Enter age:"))
if age>=18:
	print("You are eligible to vote.")
else:
	print("You are not eligible to vote.")

Write a program to display a grade based on marks.

marks=int(input("Enter marks:"))
if marks>=90:
	grade="A"
elif marks>=80:
	grade="B"
elif marks>=70:
	grade="C"
else:
	grade="F"
print("Grade:",grade)

Write a program to check whether a number is divisible by 5.

number=int(input("Enter number:"))
if number%5==0:
	print(number,"is divisible by 5.")
else:
	print(number,"is not divisible by 5.")

Write a program to find the greatest among three numbers.

a=int(input("Enter first number:"))
b=int(input("Enter second number:"))
c=int(input("Enter third number:"))
if(a>b):
	g=a
else:
	g=b
print(f"{g} is greater of {a} and {b}.")
if (g>c):
        print(f"{g} is the greatest of three numbers.")
else:
        print(f"{c} is the greatest of three numbers.")

Write a program to check whether a given year is a leap year.

year = int(input("Enter a year: "))
if (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0):
    print(f"{year} is a leap year.")
else:
    print(f"{year} is not a leap year.")

Write a program that accepts a student's marks and displays Excellent, Good, Average, or Fail according to the marks.

marks=int(input("Enter marks:"))
if marks>=90:
	remarks="Excellent"
elif marks>=80:
	remarks="Good"
elif marks>=70:
	remarks="Average"
else:
	remarks="Fail"
print(remarks)

Write a program to input three sides of a triangle and check whether the triangle is quilateral, isoceles or scalene.

a=int(input("Enter first side:"))
b=int(input("Enter second side:"))
c=int(input("Enter third side:"))
if a==b==c:
	print("Equilateral Triangle.")
elif a!=b!=c:
	print("Scalene Triangle.")
else:
	print("Isoceles Triangle.")

Write a program to input three angles of a triangle and check whether the triangle is right angled triangle or not.

a=int(input("Enter first angle:"))
b=int(input("Enter second angle:"))
c=int(input("Enter third angle:"))
if ((a+b+c==180) and (a==90 or b==90 or c==90)):
	print("Right-angled Triangle.")
else:
	print("Not Right-angled Triangle.")

Write a program to display middle number among three numbers.

num1=int(input("Enter first number:"))
num2=int(input("Enter second number:"))
num3=int(input("Enter third number:"))
if (num2 <= num1 <= num3) or (num3 <= num1 <= num2):
    middle = num1
elif (num1 <= num2 <= num3) or (num3 <= num2 <= num1):
    middle = num2
else:
    middle = num3
print(f"The middle number is {middle}.")

Write a program to display profit or loss amount.

sp=int(input("Enter selling price:"))
cp=int(input("Enter cost price:"))
if sp>cp:
	print(f"The profit amount is: {sp-cp}")
elif cp>sp:
	print(f"The loss amount is: {cp-sp}")
else:
	print("Neither Profit nor Loss.")

Part – 4 : Looping Concept

Python Looping

Introduction to Looping

In Python, a loop is used to execute a block of statements repeatedly as long as a specified condition is satisfied or for each item in a sequence.

Looping helps us perform a task multiple times without writing the same statements again and again.

Example without a loop:

print("Hello")
print("Hello")
print("Hello")
print("Hello")
print("Hello")

The same task can be performed using a loop:

for i in range(5):
    print("Hello")

Here, the print() statement is executed 5 times.

Types of Loops in Python

Python mainly provides two types of loops:

for loop
while loop

for Loop

A for loop is used to repeat a block of statements for each item in a sequence or a specified range of values.

Syntax

for variable in sequence:
    statement

Here:

for is a Python keyword.
variable stores the current value.
in is used to check values from the sequence.
sequence contains the values to be processed.
The statements inside the loop must be properly indented.

Example

for i in range(1, 6):
    print(i)

Output:

The range(1, 6) generates numbers from 1 to 5. The ending value 6 is not included.

Using for Loop with a String

A for loop can also be used to access each character of a string.

name = "Python"
for ch in name:
    print(ch)

Output:

P
y
t
h
o
n

The range() Function

The range() function is commonly used with a for loop to generate a sequence of numbers.

1. range(stop)

for i in range(5):
    print(i)

Output:

The sequence starts from 0 and ends before 5.

2. range(start, stop)

for i in range(2, 7):
    print(i)

Output:

3. range(start, stop, step)

for i in range(2, 11, 2):
    print(i)

Output:

Here, 2 is the starting value, 11 is the ending limit, and 2 is the step value.

Examples of for Loop

Display numbers from 1 to 10

for i in range(1, 11):
    print(i)

Display even numbers from 1 to 20

for i in range(2, 21, 2):
    print(i)

Output:

Find the sum of numbers from 1 to 10

total = 0
for i in range(1, 11):
    total = total + i
print("Sum =", total)

Output:

Sum = 55

Display multiplication table

n = int(input("Enter a number: "))
for i in range(1, 11):
    print(n, "x", i, "=", n * i)

Note: If the user enters 5:

5 x 1 = 5
5 x 2 = 10
...
5 x 10 = 50

while Loop

A while loop is used to repeatedly execute a block of statements as long as a given condition is True.

Syntax

while condition:
    statement

The condition is checked before every repetition.

If the condition is True, the statements inside the loop are executed.

If the condition becomes False, the loop stops.

Example of while Loop

i = 1
while i <= 5:
    print(i)
    i = i + 1

Output:

How it works

Initially, i = 1.
i <= 5 is checked.
The value of i is displayed.
i is increased by 1.
The condition is checked again.
The loop stops when i becomes 6.

Important Point in while Loop

The loop variable should generally be updated inside the loop.

i = i + 1

If we forget to update i, the condition may remain True indefinitely and create an infinite loop.

In this program, if i never changes, the condition always remains true.

Examples of while Loop

Display numbers from 1 to 10

i = 1
while i <= 10:
    print(i)
    i = i + 1

Display even numbers from 2 to 20

i = 2
while i <= 20:
    print(i)
    i = i + 2

Display numbers from 10 to 1

i = 10
while i >= 1:
    print(i)
    i = i - 1

Find the sum of numbers from 1 to 10

i = 1
total = 0
while i <= 10:
    total = total + i
    i = i + 1
print("Sum =", total)

Output:

Sum = 55

Difference Between for Loop and while Loop

for Loop	while Loop
Used when the number of repetitions or sequence is generally known.	Used when repetition depends mainly on a condition.
Commonly used with range().	Uses a condition.
The loop variable is commonly handled by the loop structure.	The loop variable usually needs to be updated manually.

Nested Loop

A nested loop is a loop inside another loop.

Example

for i in range(1, 4):
    for j in range(1, 4):
        print(i, j)

Here, the inner for loop executes for every iteration of the outer for loop.

Nested loops can be used for creating patterns and working with tables or multiple sets of data.

Loop Control with break

The break statement is used to terminate a loop immediately.

Example

for i in range(1, 11):
    if i == 6:
        break
    print(i)

Output:

When i becomes 6, the loop stops.

Loop Control with continue

The continue statement skips the remaining statements of the current iteration and moves to the next iteration.

Example

for i in range(1, 6):
    if i == 3:
        continue
    print(i)

Output:

The number 3 is skipped.

Programming Questions

Write a Python program to display numbers from 1 to 20 using a for loop.
Write a Python program to display all even numbers from 1 to 50 using a for loop.
Write a Python program to display all odd numbers from 1 to 50 using a while loop.
Write a Python program to calculate the sum of numbers from 1 to 100.
Write a Python program to display the multiplication table of a number entered by the user.
Write a Python program to calculate the sum of even numbers from 1 to 50.
Write a Python program to display numbers from 20 to 1 in reverse order.
Write a Python program to find the factorial of a number using a while loop.
Write a Python program to display each character of a word entered by the user.
Write a Python program using nested loops to display the following pattern:

		*
		**
		***
		****
		*****