Making Decisions with Conditions

Learning Objectives: After this lesson, you'll learn to control program flow with if statements, master comparison and logical operators, and understand how Python evaluates boolean expressions.

Introduction to Conditional Logic

Programs need to make decisions based on different situations. Python uses conditional statements to execute different code paths depending on whether conditions are true or false.

Think of it like a flowchart in your daily life:

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

Basic If Statements

The simplest conditional statement is the if statement:

Key Points:

• The condition must evaluate to True or False
• Code inside the if block is indented (usually 4 spaces)
• If the condition is False, the indented code is skipped

If-Else Statements

Use else to specify what happens when the condition is False:

If-Elif-Else Chains

For multiple conditions, use elif (else if):

Comparison Operators

Python provides several operators to compare values:

Logical Operators

Combine multiple conditions using logical operators:

Truthiness in Python

Python considers some values as "falsy" and others as "truthy":

Nested Conditions

You can put if statements inside other if statements:

Practical Examples

Example 1: User Authentication System

Example 2: Shipping Calculator

Practice Exercises

Exercise 1: Age Category Classifier

Exercise 2: Grade Calculator with Validation

Key Takeaways

✅ If statements control program flow based on conditions
✅ Indentation matters - Python uses indentation to group code blocks
✅ Comparison operators (==, !=, <, >, <=, >=) compare values
✅ Logical operators (and, or, not) combine conditions
✅ Truthiness - Empty containers and zero values are "falsy"
✅ elif chains handle multiple exclusive conditions
✅ Nested conditions allow complex decision trees

Next Steps

In the next lesson, we'll learn about loops and iteration - how to repeat operations efficiently using for and while loops, and control loop execution with break and continue.

Ready to make your code repeat tasks automatically? The next lesson will show you the power of loops!