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PAMSPervez Akhtar Memorial Solution

Programming Fundamentals · Lesson 07

Reusable functions

Package a calculation into a named function with a parameter and a return value.

Author: HumaPervez 7 min read Free access

A function groups instructions under a name. Define one with def, choose a descriptive name, and place its parameters in parentheses. A parameter stands for a value that a caller supplies later.

Calling a function runs its instructions. A return statement sends a result back to the caller. The caller can store that result, use it in another expression, or print it.

Our workshop needs two cups per visitor. Putting the calculation in one function gives the rule one place to live even when several groups need supplies.

Read the example

Python 3
def cups_needed(people):
    return people * 2

morning = cups_needed(4)
afternoon = cups_needed(6)
print(morning + afternoon)
Expected output
20

The first call returns 8 and the second returns 12. The last line adds the two values. Keeping print outside the function lets another caller reuse the calculation without displaying anything.

Try it yourself

Write a function called pencils_needed that takes a group size and returns three pencils per person. Call it with 7 and print the result.

Show a worked solution 
def pencils_needed(people):
    return people * 3

print(pencils_needed(7))  # 21

Check your understanding

Your lesson quiz

Answer all five questions. Score at least 4 out of 5 (80%) to pass. You can retry as often as you like.

1. Which keyword defines a function in Python?
2. What does return do?
3. If cups_needed returns people * 2, what is cups_needed(6)?
4. What is a parameter?
5. Why can keeping print outside a calculation function help?

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