Conditional Execution — Lesson 1: Make a choice with if

New skill: If statements and indentation
Previously learned: Unit 04 — comparisons and Boolean logic

Why this matters

Programs can make a choice based on a Boolean expression. Python executes the indented body of an if statement only when its condition is true.

Study this example

def warning(battery):
    message = 'Ready'
    if battery < 20:
        message = 'Charge needed'
    return message

For warning(15) the condition is true, so the message changes. For warning(90) Python skips the indented assignment and returns ‘Ready’. The colon and indentation are required.

Before moving on, predict the result of the program or function. Then run it and compare.

Check your understanding

What would warning(20) return? What does the indentation tell Python?

Common mistake

The colon after if and the indentation underneath it are part of Python syntax.

Practice

Complete classify_temperature(temperature) so it returns 'Cold alert' for temperatures below 10, and 'Normal' otherwise.

Public example 1

Input

classify_temperature(5)

Output

'Cold alert'

Public example 2

Input

classify_temperature(10)

Output

'Normal'

Public example 3

Input

classify_temperature(-4)

Output

'Cold alert'

Open the Python starter

Hint 1

Choose the comparison for below 10.

Hint 2

Only update `message` when your condition is true.

Hint 3

Keep `return message` after the conditional block.

Reflection

Explain why your solution works and describe one boundary case you tried.