Conditionals and Input

Conditionals allow our program to make decisions using if, elif, and else to control the flow of execution. Only the first True branch in a chain will execute.

Normalizing Input​

When accepting text from a user, always use .strip().lower() to clean it up first. This prevents bugs caused by extra spaces or unexpected capitalization during comparisons.

# Assuming user enters " Medium "
user_input = input("Choose a size (Small/Medium/Large): ").strip().lower()

if user_input == "small":
    price = 10
elif user_input == "medium":
    price = 30
else:
    price = 50

print(f"Price: {price}")

Choose a size (Small/Medium/Large):  Medium
Price: 30

Nested Conditionals​

Use nested if statements for checks that depend on a previous result.

device_status = "active"
temp = 38

if device_status == "active":
    if temp > 35:
        print("Warning: High temperature!")
    else:
        print("Temperature is normal")
else:
    print("System is offline.")

Warning: High temperature!

The Ternary Operator​

For simple assignments, a one-line ternary expression is more Pythonic. It allows for simple if/else assignments that read like an English sentence.

order_total = 320

# format: [value_if_true] if [condition] else [value_if_false]
delivery_fee = 0 if order_total > 300 else 30

print(f"Delivery fee: {delivery_fee}")

Delivery fee: 0

Converting Types for Comparisons​

Remember that input() always returns a string. We must explicitly cast it for numeric comparisons.

# Assuming user enters "20"
age = int(input("Enter our age: "))
if age >= 18:
    print("Access granted.")

Enter our age: 20
Access granted.