Chapter 9a - Functions

A function is a named block you can call. def defines it. return sends a value back to the caller.

def greet(name):
    return "Hello, " + name

print(greet("Ada"))

🧪 Try it yourself

Add a second function that returns n * 10.

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Parameters and return

Arguments fill parameters when you call the function. If you print inside the function, that is a side effect. Prefer return when you need a value for later math or tests.

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

total = add(3, 5)
print(total)

🧪 Two parameters

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Mini quiz — def and return

Quiz

def and return

1 / 2

What does this print?

def f():
  return 2
print(f() + 3)

Pick an answer to see if you are right.

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Challenge: double

Write double(n) so it returns twice n.

n	Return
4	8
-3	-6

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Default arguments and local variables

def greet(name, punctuation="!"):
    return "Hi " + name + punctuation

print(greet("Lin"))
print(greet("Lin", "?"))

Variables created inside a function are local. They disappear when the function ends.

🧪 Defaults

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Mini quiz — defaults and scope

Quiz

Defaults and scope

1 / 2

What is greet("Ada")?

def greet(name, p="!"):
  return name + p

Pick an answer to see if you are right.

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Challenge: in range

Write in_range(n, low, high) so it returns True if n is between low and high inclusive, otherwise False.

n	low	high	Return
5	1	10	True
0	1	10	False

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Exercises

Activity: Count vowels

Write count_vowels(text) so it returns how many characters are in aeiouAEIOU.

Expected for Hello:

2