Conditional Statements

Overview

Conditional statements allow your program to make decisions and execute different blocks of code based on conditions.

Learning Objectives

• Write decision blocks using if, elif, and else.
• Understand truthiness and falsiness of basic objects.
• Use short inline conditional expressions.

Concept Explanation

Conditionals evaluate statements from top to bottom. Once a condition is met, that block runs and execution skips the rest. Objects have inherent truthiness: empty lists or empty text strings evaluate to False, while populated ones evaluate to True.

Code Examples

Example 1 — Basics

This example introduces the fundamental syntax and concepts.

score = 85
if score >= 90:
    print('Grade: A')
elif score >= 80:
    print('Grade: B')
else:
    print('Grade: C')

Example 2 — Everyday Usage

This example demonstrates a realistic scenario handling business parameters.

# Check if items cart is empty
cart_items = []
if not cart_items:
    print('Your shopping cart is empty.')
else:
    print(f'You have {len(cart_items)} items in your cart.')

Example 3 — Advanced Example

This example shows clean, production-grade code structure following senior development standards.

# Set status message using inline conditional expression
user_logged_in = True
status_msg = 'Welcome back!' if user_logged_in else 'Please sign in.'
print(status_msg)

Visual Flow

The following execution flow represents the step-by-step evaluation inside the interpreter:

Evaluate condition check → If True, run block → Skip remaining elif/else → Continue program

Common Mistakes

Review these common pitfalls when working with this topic:

• Forgetting the colon (:) character at the end of if, elif, or else statements.
• Using a single equals sign (=) instead of double equals (==) inside conditions.
• Comparing boolean variables explicitly to True or False (e.g. if is_active == True:).
• Writing misaligned indentation blocks inside conditions.

Best Practices

Enforce these Pythonic best practices in your codebase:

if value == True:
    status = 'active'
else:
    status = 'inactive'

status = 'active' if value else 'inactive' # Clean inline ternary

Quick Revision

Use these key summaries for last-minute revision:

• if initiates a conditional check block.
• elif checks additional conditions if previous ones failed.
• else runs if no prior conditions were met.
• Indent code blocks to show what code belongs to each branch.
• Empty strings, empty lists, 0, and None are considered False.