Welcome back, Python learner!
In Post 3, we explored Operators and Expressions — how to perform calculations, compare values, and make logical decisions.
Now, it’s time to take your programs to the next level:
We’ll learn how to make Python think and decide using Conditional Statements.
What Are Conditional Statements?
Conditional statements allow your program to make decisions based on certain conditions.
For example:
“If it’s raining, take an umbrella; otherwise, don’t.”
In Python, we use the if, elif, and else keywords to write such logic.
Basic Structure of if Statement
if condition:
# code block
If the condition is True, the indented code block runs.
If the condition is False, Python skips that block.
Example:
age = 18
if age >= 18:
print(“You are eligible to vote.”)
Output:
You are eligible to vote.
If age was less than 18, nothing would print because the condition would be False.
The if-else Statement
What if we want to run one block when the condition is True,
and another block when it’s False?
That’s where else comes in!
if condition:
# if True
else:
# if False
Example:
age = int(input(“Enter your age: “))
if age >= 18:
print(“You can vote!”)
else:
print(“Sorry, you are too young to vote.”)
Output Example 1:
Enter your age: 20
You can vote!
Output Example 2:
Enter your age: 15
Sorry, you are too young to vote.
The if-elif-else Ladder
Sometimes, you have multiple conditions to check.
In that case, we use elif (short for else if).
if condition1:
# code
elif condition2:
# code
else:
# code
Example:
marks = int(input(“Enter your marks: “))
if marks >= 90:
print(“Grade: A+”)
elif marks >= 80:
print(“Grade: A”)
elif marks >= 70:
print(“Grade: B”)
elif marks >= 60:
print(“Grade: C”)
else:
print(“Grade: F”)
Output Example:
Enter your marks: 85
Grade: A
Nested if Statements
You can place one if statement inside another — this is called a nested if.
Example:
age = int(input(“Enter your age: “))
if age >= 18:
print(“You are an adult.”)
if age >= 60:
print(“You are also a senior citizen.”)
else:
print(“You are not a senior citizen yet.”)
else:
print(“You are a minor.”)
Output Example:
Enter your age: 65
You are an adult.
You are also a senior citizen.
Combining Conditions with Logical Operators
You can also combine multiple conditions using and, or, and not (from the previous lesson).
Example 1:
age = 25
has_id = True
if age >= 18 and has_id:
print(“You can enter the club.”)
else:
print(“Access denied.”)
Example 2:
day = “Sunday”
if day == “Saturday” or day == “Sunday”:
print(“It’s weekend!”)
else:
print(“It’s a weekday.”)
Using if with Strings and Lists
Python allows you to use conditions with strings, lists, and other data types too.
Example 1:
name = input(“Enter your name: “)
if name == “Alice”:
print(“Welcome, Alice!”)
else:
print(“Hello, stranger!”)
Example 2:
fruits = [“apple”, “banana”, “mango”]
if “apple” in fruits:
print(“Yes, apple is available!”)
else:
print(“No, apple is not in the list.”)
Real-Life Example: Simple Calculator
Let’s combine everything we’ve learned so far — operators, input, and conditions.
Code Example:
num1 = float(input(“Enter first number: “))
num2 = float(input(“Enter second number: “))
op = input(“Enter operator (+, -, *, /): “)
if op == “+”:
print(“Result:”, num1 + num2)
elif op == “-“:
print(“Result:”, num1 – num2)
elif op == “*”:
print(“Result:”, num1 * num2)
elif op == “/”:
if num2 != 0:
print(“Result:”, num1 / num2)
else:
print(“Error: Division by zero!”)
else:
print(“Invalid operator!”)
Sample Run:
Enter first number: 10
Enter second number: 5
Enter operator (+, -, *, /): *
Result: 50.0
Practice Tasks
Try solving these challenges
Write a program to check whether a number is positive, negative, or zero.
Take a user’s age and check:
If the user is a child (<13)
A teenager (13–19)
An adult (20–59)
Or a senior citizen (60+)
Ask the user for a year and determine if it’s a leap year or not.
Bonus: Create a login system that checks if username and password match preset values.
Summary
You learned:
How to use if, elif, and else to make decisions
How to nest conditions and use logical operators
How to write real-world programs that react to user input
Conditional statements are the foundation of logic in programming — every smart program you’ll ever build depends on them!
