Week 10: Functions

A function is a named block of code that you define once and call whenever you need it. In Python you start a function with the word def, then write its name followed by inputs inside parentheses. This week you use the parentheses you learned earlier in a new context, and you add commas between the inputs. The body of the function is indented, just as in a loop.

What you will learn

On the US English layout, the three symbols are typed like this:

• ( is the 9 key held with Shift. Hold Shift with the opposite pinky and press 9 with the right ring finger.
• ) is the 0 key held with Shift. Hold Shift with the opposite pinky and press 0 with the right pinky.
• , is the comma key, pressed with the right middle finger.

Here is a short function that takes two inputs:

def add(a, b):
    return a + b

The first line names the function add and lists two inputs, a and b. The comma separates them. The second line returns the sum and is indented by four spaces.

Technique tips

• As soon as you type the opening parenthesis, think of the closing one. Keep your eyes on the end of the line.
• Put a space after each comma. The space makes the inputs easier to read and to check.
• Press Shift with the opposite pinky before the parentheses, and release both after the symbol appears.
• The colon at the end of the def line is required. The body starts on the line below it.
• Say the function name once in your head before typing it. Knowing the name reduces spelling errors in later calls.

Lessons

1. Lesson 1 (10 to 15 minutes): Learn. Watch the keyboard demo for the parentheses and the comma. Then type def add(a, b): slowly.
2. Lesson 2 (10 to 15 minutes): Practice. Repeat return a + b with its indentation. Check that the parentheses and commas match in every line.
3. Lesson 3 (10 to 15 minutes): Review. Take the 2-minute test built from this week’s function lines. Note any line where a bracket or comma went missing and repeat it next time.

This week’s goal

The goal is 19 wpm with 93% accuracy. The first star comes when you finish the lessons. The second star comes at 93% accuracy, and the third when you also reach 19 wpm. A missing parenthesis or comma spoils the whole definition, so accuracy comes first.