Python Programming

python condition

Python Conditional Statements

Introduction

Programs often need to make decisions.

Examples:

  • If age is 18 or more → Allow voting
  • If marks are above 40 → Pass
  • If balance is sufficient → Allow withdrawal
  • If password is correct → Login

Conditional statements allow programs to make decisions.

What is a Conditional Statement?

A conditional statement executes code only when a condition is True.

Example:

age = 20

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

Output:

Eligible to vote

Understanding Conditions

A condition always evaluates to:

True

or

False

Examples:

print(10 > 5)
print(10 < 5)

Output:

True
False

Types of Conditional Statements

Python provides:

  1. if
  2. if-else
  3. if-elif-else
  4. Nested if
  5. Multiple if Statements
  6. Conditional Expressions (Ternary Operator)

The if Statement

Used when a block should run only if a condition is True.

Syntax:

if condition:
    statement

Example:

age = 18

if age >= 18:
    print("You can vote")

Output:

You can vote

if Condition False

age = 15

if age >= 18:
    print("You can vote")

Output:

No output

Because condition is False.

Flow of if Statement

Condition
    ↓
True ? ---- Yes ----> Execute Block
    |
    No
    ↓
 Skip Block

Multiple Statements Inside if

age = 20

if age >= 18:
    print("Adult")
    print("Can vote")
    print("Can apply for license")

Output:

Adult
Can vote
Can apply for license

if-else Statement

Used when exactly one of two choices should execute.

Syntax:

if condition:
    code
else:
    code

Example

age = 16

if age >= 18:
    print("Eligible")
else:
    print("Not Eligible")

Output:

Not Eligible

Real Life Example

password = "python123"

if password == "python123":
    print("Login Successful")
else:
    print("Wrong Password")

Output:

Login Successful

Flow of if-else

Condition
    ↓
True ? ---- Yes ----> if Block
    |
    No
    ↓
else Block

if-elif-else Statement

Used when there are multiple conditions.

Syntax:

if condition1:
    code

elif condition2:
    code

elif condition3:
    code

else:
    code

Example

marks = 85

if marks >= 90:
    print("Grade A+")

elif marks >= 80:
    print("Grade A")

elif marks >= 70:
    print("Grade B")

else:
    print("Grade C")

Output:

Grade A

Important Rule

Only the first matching condition executes.

Example:

marks = 95

if marks >= 90:
    print("A+")

elif marks >= 80:
    print("A")

elif marks >= 70:
    print("B")

Output:

A+

Remaining conditions are skipped.

Grade Calculator Example

marks = 72

if marks >= 90:
    print("A+")

elif marks >= 80:
    print("A")

elif marks >= 70:
    print("B")

elif marks >= 60:
    print("C")

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

else:
    print("Fail")

Output:

B

Multiple if Statements

Each condition is checked independently.

Example:

age = 25

if age > 10:
    print("Greater than 10")

if age > 20:
    print("Greater than 20")

if age > 30:
    print("Greater than 30")

Output:

Greater than 10
Greater than 20

Difference Between if-elif and Multiple if

if-elif

Only one block executes.

score = 95

if score >= 90:
    print("Excellent")

elif score >= 80:
    print("Very Good")

Output:

Excellent

Multiple if

All matching blocks execute.

score = 95

if score >= 90:
    print("Excellent")

if score >= 80:
    print("Very Good")

Output:

Excellent
Very Good

Nested if Statement

An if inside another if.

Syntax:

if condition1:

    if condition2:
        code

Example

age = 20

citizen = True

if age >= 18:

    if citizen:
        print("Eligible to vote")

Output:

Eligible to vote

Nested if-else Example

age = 20

if age >= 18:

    print("Adult")

    if age >= 21:
        print("Can enter club")
    else:
        print("Cannot enter club")

else:
    print("Minor")

Output:

Adult
Cannot enter club

Multi-Level if Statement

A multi-level if means decisions occurring in multiple layers.

Example:

username = "admin"
password = "1234"

if username == "admin":

    if password == "1234":
        print("Login Successful")

    else:
        print("Wrong Password")

else:
    print("Wrong Username")

Output:

Login Successful

Multi-Level Banking Example

balance = 10000
withdraw = 5000

if balance > 0:

    if withdraw <= balance:
        print("Transaction Successful")

    else:
        print("Insufficient Balance")

else:
    print("Account Empty")

Output:

Transaction Successful

Using Logical Operators in Conditions

and

Both conditions must be True.

age = 20
citizen = True

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

Output:

Eligible

or

At least one condition must be True.

marks = 35
sports_quota = True

if marks >= 40 or sports_quota:
    print("Selected")

Output:

Selected

not

Reverses True and False.

is_banned = False

if not is_banned:
    print("Access Granted")

Output:

Access Granted

Comparison Operators Used in Conditions

Operator Meaning
== Equal
!= Not Equal
> Greater Than
< Less Than
>= Greater Than or Equal
<= Less Than or Equal

Truthy and Falsy Values

Python treats some values as False.

Falsy values:

False
None
0
0.0
''
[]
{}
set()

Example:

name = ""

if name:
    print("Name Found")
else:
    print("Empty")

Output:

Empty

Ternary Operator (Conditional Expression)

Short form of if-else.

Syntax:

value_if_true if condition else value_if_false

Example:

age = 20

message = "Adult" if age >= 18 else "Minor"

print(message)

Output:

Adult

Common Mistakes

Mistake 1: Using = Instead of ==

❌ Wrong

if age = 18:

Output:

SyntaxError

✅ Correct

if age == 18:

Mistake 2: Missing Colon

❌ Wrong

if age >= 18
    print("Adult")

Output:

SyntaxError

✅ Correct

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

Mistake 3: Incorrect Indentation

❌ Wrong

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

Output:

IndentationError

✅ Correct

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

Mistake 4: Using Multiple if Instead of if-elif

❌ Wrong

marks = 95

if marks >= 90:
    print("A+")

if marks >= 80:
    print("A")

Output:

A+
A

Sometimes only one grade is expected.

✅ Better

if marks >= 90:
    print("A+")

elif marks >= 80:
    print("A")

Mistake 5: Wrong Range Logic

❌ Wrong

age = 20

if age >= 18 or age <= 60:
    print("Working Age")

This condition is almost always True.

✅ Correct

if age >= 18 and age <= 60:
    print("Working Age")

Mistake 6: Comparing Different Data Types

❌ Wrong

age = input("Enter Age: ")

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

Output:

TypeError

✅ Correct

age = int(input("Enter Age: "))

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

Best Practices

Keep Conditions Simple

❌ Avoid

if (((age >= 18 and citizen == True) and verified == True)):

✅ Better

if age >= 18 and citizen and verified:

Use Meaningful Variables

is_logged_in = True
is_verified = True

if is_logged_in and is_verified:
    print("Access Granted")

Use if-elif for Multiple Choices

if grade == "A":
    pass

elif grade == "B":
    pass

else:
    pass

Homework 1

Check whether a number is positive.

Solution

number = 10

if number > 0:
    print("Positive")

Homework 2

Check whether a number is even or odd.

Solution

number = 7

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

Homework 3

Create a grade calculator.

Rules:

90+ = A+
80+ = A
70+ = B
60+ = C
Below 60 = Fail

Solution

marks = 85

if marks >= 90:
    print("A+")

elif marks >= 80:
    print("A")

elif marks >= 70:
    print("B")

elif marks >= 60:
    print("C")

else:
    print("Fail")

Homework 4

Check voting eligibility.

Conditions:

Age >= 18
Citizen = True

Solution

age = 20
citizen = True

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

else:
    print("Not Eligible")

Homework 5

Create a login system.

Requirements:

Username = admin
Password = 1234

Use nested if.

Solution

username = "admin"
password = "1234"

if username == "admin":

    if password == "1234":
        print("Login Successful")

    else:
        print("Wrong Password")

else:
    print("Wrong Username")

Homework 6

Use a ternary operator to determine whether a person is Adult or Minor.

Solution

age = 17

result = "Adult" if age >= 18 else "Minor"

print(result)

Output:

Minor

Homework 7

Check whether a year is a leap year.

Hint:

year % 4 == 0

Solution

year = 2024

if year % 4 == 0:
    print("Leap Year")
else:
    print("Not Leap Year")

Quick Revision

Statement Purpose
if Execute when True
if-else Choose between two options
if-elif-else Multiple choices
Nested if Decision inside another decision
Multiple if Check all conditions
Ternary Operator Short if-else

Conditional Statement Flow

if
│
├── True → Execute
│
└── False → Skip


if-else
│
├── True → if block
│
└── False → else block


if-elif-else
│
├── Condition 1
├── Condition 2
├── Condition 3
└── else

Summary

Concept Description
if Executes when condition is True
else Executes when condition is False
elif Additional conditions
Nested if if inside another if
Multi-Level if Decision tree structure
Logical Operators and, or, not
Comparison Operators ==, !=, >, <, >=, <=
Ternary Operator One-line if-else
Truthy/Falsy Values treated as True or False

Conditional statements are the foundation of decision-making in Python and are heavily used in:

  • Login Systems
  • Banking Applications
  • Games
  • Web Applications
  • APIs
  • Data Validation
  • Automation Scripts

Master conditional statements before moving to loops (for and while) because loops frequently depend on conditions.

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