Python Conditional Statements

:dart: Learning Objectives

By the end of this lesson, you will be able to:

• Understand what conditional statements are and why we use them
• Use comparison operators to create conditions
• Apply logical operators to combine conditions
• Write if, if-else, and if-elif-else statements
• Create programs that make decisions based on user input

:information_source: What are Conditional Statements? Conditional statements are rules that check conditions before executing or skipping blocks of code. They help your program make decisions!

:bar_chart: How Python Normally Runs Code

Python usually follows a sequential flow. This means it reads and runs your code line by line, from top to bottom.

Sequential flow example:

         ┌─────────┐
         (  Start  )
         └────┬────┘
              │
              ▼
         ┌─────────┐
         │  a = 5  │
         └────┬────┘
              │
              ▼
         ┌─────────┐
         │  b = 7  │
         └────┬────┘
              │
              ▼
         ┌─────────┐
         │ c = a+b │
         └────┬────┘
              │
              ▼
         ┌─────────┐
         │ print(c)│
         └────┬────┘
              │
              ▼
         ┌─────────┐
         (   End   )
         └─────────┘

:emoji: Why Do We Need Conditional Statements?

Think about real life - you make decisions every day!

• If it's raining, you take an umbrella
• If you're hungry, you eat
• If it's late, you go to sleep

In programming, we need our code to make similar decisions. Conditional statements let our programs:

• Check conditions
• Make choices
• Run different code based on those choices

:bulb: Real-World Example Imagine a game where players must be at least 13 years old to play. Your program needs to check the player's age before letting them start!

:wrench: Components of Conditional Statements

Every conditional statement has two main parts:

One. Condition

A test that results in either True or False (called a Boolean expression)

2. Code Block

The code that runs based on the condition:

• If the condition is True -> the code runs :white_check_mark:
• If the condition is False -> the code is skipped :x:

Basic Structure

Here's how an if statement looks:

if condition:
    # This code runs if condition is True

:memo: Important! The colon (:) and indentation are required in Python. The indented code is the "code block" that runs when the condition is True.

To create conditions, we use two types of operators: Comparison and Logical.

:mag: Comparison Operators

Comparison operators compare two values and return True or False:

:warning: Common Mistake! Don't confuse = with ==:

• = assigns a value to a variable (like age = 15)
• == compares two values (like age == 15)

:link: Logical Operators

Logical operators combine multiple conditions together:

:bulb: Remember!

• and: Both must be True :white_check_mark: AND :white_check_mark:
• or: At least one must be True :white_check_mark: OR :x:
• not: Flips the result :emoji:

:books: Types of Conditional Statements

Let's explore different types of conditional statements:

1. If Statement - Runs code when a condition is True
2. If-else Statement - Chooses between two options
3. If-elif-else Statement - Chooses between multiple options
4. Combined Conditions - Uses logical operators for complex decisions

1️⃣ If Statement

The simplest conditional statement. It runs code only when a condition is True.

Structure:

if condition:
    # Code runs if condition is True

Example: Age Check

age = 20
if age > 17:
    print("You cannot join this class")
    print("This class only for below 16 years old ")

Expected output:

You cannot join this class
This class only for below 16 years old

What happens:

1. age is set to 20
2. Python checks: Is age > 17? (Is `20 > 17`?)
3. The answer is True, so the print statements run

:memo: Try It! Change age to 15 and run the code again. What happens? Nothing prints because 15 is not greater than 17!

3️⃣ If-elif-else Statement

When you have multiple conditions to check, use elif (short for "else if").

Structure:

if condition1:
    # Runs if condition1 is True
elif condition2:
    # Runs if condition1 is False AND condition2 is True
elif condition3:
    # Runs if both above are False AND condition3 is True
else:
    # Runs if all conditions are False

Example: Multiple Age Groups

age = 15

if age == 13:
    print("You are 13 years old")
elif age == 14:
    print("You are 14 years old")
elif age == 15:
    print("You are 15 years old")
elif age == 16:
    print("You are 16 years old")
else:
    print("Please enter age in range 13 - 16")

Expected output:

You are 15 years old

How it works:

1. Python checks each condition in order
2. When it finds a True condition, it runs that code block
3. It then skips all remaining conditions
4. If no conditions are True, the else block runs

In this example:

• Is age 13? No :x:
• Is age 14? No :x:
• Is age 15? Yes! :white_check_mark: -> Prints "You are 15 years old"
• The remaining conditions are skipped

4️⃣ Combining Conditions

Use logical operators (and, or) to create more complex conditions.

Why combine conditions?

• Check if a number is in a range
• Test multiple requirements at once
• Write cleaner, shorter code

Example: Age Categories

age = 17

if age >= 10 and age <= 12:
    print("You are the youngest student")
elif age >= 13 and age <= 15:
    print("You are in the middle")
elif age >= 16 and age <= 17:
    print("You are the senior in school")
else:
    print("Please insert the correct age")

Expected output:

You are the senior in school

How the and operator works:

• For age >= 16 and age <= 17 to be True:
  • BOTH conditions must be True
  • Is ``17 >= 16``? Yes :white_check_mark:
  • Is ``17 <= 17``? Yes :white_check_mark:
  • Both are True, so the whole condition is True!

:bulb: Range Checking Using and is perfect for checking if a value is within a range:

• age >= 10 and age <= 12 -> Is age between 10 and 12?
• score >= 80 and score <= 100 -> Is score between 80 and 100?

:memo: Summary

Key Concepts Learned:

1. Conditional statements let programs make decisions
2. Comparison operators (==, !=, <, >, <=, >=) compare values
3. Logical operators (and, or, not) combine conditions
4. If statements run code when conditions are True
5. If-elif-else chains check multiple conditions in order

Remember:

• Always use : after conditions
• Indent the code blocks properly
• Conditions are checked from top to bottom
• Only one block runs in an if-elif-else chain

:movie_camera: Video

:emoji: AI Prompt

Code with AI: Try using AI to work with conditional statements.

Prompts:

• "Help me write an if-else statement to check if a number is positive or negative."
• "Create a program that determines if a person is eligible to vote based on their age."
• "Write a nested if statement to categorize a student's grade (A, B, C, D, F)."

:dart: Practice Challenges

Challenge One: Temperature Checker

Write a program that:

• Asks for the temperature
• Prints "It's cold!" if ``temperature < 10``
• Prints "Nice weather!" if temperature is between 10-25
• Prints "It's hot!" if ``temperature > 25``

Challenge 2: Password Validator

Create a program that:

• Asks for a password
• Checks if the password length is at least 8 characters
• Prints whether the password is valid or too short

Challenge 3: Grade Calculator

Build a program that:

• Takes a test score (0-100)
• Assigns a letter grade (A: 90-100, B: 80-89, C: 70-79, D: 60-69, F: below 60)
• Prints the grade with an encouraging message