A song sheet
The chorus is written once. Then the sheet just says "Chorus" again.
11CLEAN CODE · DON'T REPEAT
Write it once, use it often.
When lines repeat, a loop or a function can do the work: same output, shorter and safer code.
IN REAL LIFE
Do it once, use it again.
People find smart ways to avoid doing the same work twice.
A teacher's stamp
She doesn't draw each star by hand. One stamp makes the same star every time.
A pancake recipe
"Repeat for each pancake" instead of writing the steps ten times.
LOOK FIRST
Spot it, then clean it.
Same lines? Loop
Three print("Hooray!") lines become one for loop with range(3).
Small changes? Function
When only a name changes, write a function with a parameter for it.
Fix one place
The lines live in one spot. Change them once and every use changes.
LOOK FIRST
Read the clean version.
Two welcomes, but the lines are written only once.
def welcome(name):One function. The parameter name is the part that changes. print("Hi, " + name + "!")Written once, used for everyone. print("Welcome to the team.")Change this line once, and every welcome changes.welcome("Ana")Runs both lines with name = "Ana".welcome("Leo")The same lines again, now for Leo.RUN IT
PyBot cheers for the team.
Guess first. Then run real Python and check.
Guess the result
def cheer(name):
print("Go, " + name + "!")
for friend in ["Ana", "Leo", "Mia"]:
cheer(friend)What will Python show?
OUTPUT
PyBot's hint
Ready. Press Run Python.
Python runs here thanks to Pyodide ♥
Pyodide 314.0.3 runs CPython in your browser with WebAssembly.
Open-source under the Mozilla Public License 2.0. License
Now change one thing: Change "Go, " to "Yay, " in one place and run. All three lines change!
YOUR TURN
Spot the repeat.
Try each tiny question. A wrong answer becomes something to review.
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0Review
Like a song
A song has the same chorus 3 times.
What is the cleanest song sheet?
Same lines
print("Brush teeth")
print("Brush teeth")
print("Brush teeth")Which cleaner code shows the same output?
Inside the loop
for i in range(4):
print("Jump!")
print("Rest")How many repeated print lines does this loop replace?
Only the name changes
print("Happy birthday, Ana!")
print("Happy birthday, Leo!")
print("Happy birthday, Mia!")What is the best tool to clean this up?
Call the function
def birthday(name):
print("Happy birthday, " + name + "!")
birthday("Leo")What will Python show?
One fix
A greeting lives inside one function. The program calls it 5 times. Now the greeting must change.
How many places do you edit?
Why clean it?
Messy code and clean code show exactly the same output.
So why clean it?
Fix PyBot's code
PyBot changed the snack from cookies to apples, but missed one copy. Write a function so the snack lives in one place, and match the goal.
Goal output
Ana gets an apple. Thanks, PyBot! Leo gets an apple. Thanks, PyBot! Mia gets an apple. Thanks, PyBot!OUTPUT
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BIG IDEA
Don't Repeat Yourself.
Repeated lines become a loop. Repeated chunks with small changes become a function with a parameter. Then one fix fixes everything.