Making a sandwich
Get the bread, add the filling, close it, cut it. Four small jobs.
10THINK LIKE A PROGRAMMER · SPLIT IT
Split big problems into pieces.
A big problem is many small problems together. Solve one small piece at a time.
IN REAL LIFE
Big jobs are small jobs.
You already split big jobs every day.
Cleaning your room
First the toys, then the clothes, then the books. Much easier!
A big LEGO set
The box has numbered bags. You build bag 1, then bag 2, then bag 3.
LOOK FIRST
How programmers split a problem.
Find the pieces
Ask: what small jobs make up the big job?
Solve one piece
Make one piece work and check it before the next one.
Join the pieces
Put the pieces in order. Each piece uses what the one before made.
Remember? At the start of the course you made tiny plans in steps. Now each step becomes Python. Thinking in steps
LOOK FIRST
A tiny shop in four pieces.
Each line is one piece of the shop program.
prices = [3, 5, 4]Piece 1: keep the prices in a list.total = total + pricePiece 2: inside a loop, add each price to the total.total = total - 2Piece 3: if the total is 10 or more, take 2 coins off.print("You pay", total, "coins")Piece 4: tell the customer how much to pay.RUN IT
Run the whole shop.
Guess first. Then run real Python and check.
Guess the result
# Piece 1: the prices
prices = [3, 5, 4]
# Piece 2: add them up
total = 0
for price in prices:
total = total + price
# Piece 3: the discount
if total >= 10:
total = total - 2
# Piece 4: the message
print("You pay", total, "coins")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 the prices to [1, 2, 3] and run again. Does the discount piece still work?
YOUR TURN
Find the pieces.
Try each tiny question. A wrong answer becomes something to review.
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0Review
Like a LEGO set
You get a LEGO castle with 300 pieces in numbered bags.
Which plan splits the job into pieces?
Why split it?
PyBot wants to write a quiz game with questions, points, and a final score.
Why does PyBot split it into pieces?
Which piece first?
A game program: start the score, add points for each win, show the score.
Which piece must come before adding points?
Name the piece
total = total + priceWhich piece of the shop does this line do?
The missing piece
prices = [2, 6]
for p in prices:
total = total + p
print("You pay", total)NameError: name 'total' is not defined
Which piece is missing before the loop?
Check one piece
Your shop shows the wrong total. The prices piece looks fine.
What is a smart next step?
A good piece
Pieces of a birthday program: count the guests, buy the cake, send the invitations.
What makes a good small piece?
Add the missing piece
Piece 3 is missing. Big buys of 10 coins or more get 2 coins off. Add it and match the goal.
Goal output
You pay 9 coinsOUTPUT
Put the pieces in order
The message piece runs too early. Move the pieces so each one comes after the piece it needs.
Goal output
You pay 7 coinsOUTPUT
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BIG IDEA
Big problems are small problems together.
Find the pieces, solve one at a time, check each one, then join them in order.