Week 11 · Tuesday: Plan your capstone (Code Crew G5)

Tuesday: Break it into parts

Rocket opens a blank file for the inventory tracker. He stares at it. "Where do I even start?"

Raven draws a box labeled Tracker. Under it she draws smaller boxes. "What do you notice about my drawing?"

"It is a tree!" Rocket says. "The whole job is the root, and each part is a child."

"And each part is small enough to build in one sitting," Raven says.

Nova hums. "Here is a hint. Give each small part its own function."

Decompose the tracker

To decompose a problem means to break it into smaller parts. Each part becomes one function with one job.

Part	Job	Function
Count	Add up every supply	total_items(stock)
Low	List the supplies below a limit, in A to Z order	low_stock(stock, limit)
Find	Find an item in a sorted list of names, fast	find_item(names, target)
Crew	Count everyone in the command tree	count_crew(node)
Restock	Add more of a supply	restock(stock, item, amount)
Report	Print everything clearly	report(stock, tree)

Tracker

↓

Data: supplies and crew tree

↓

Helpers: total, low, find, crew, restock

↓

Tests

↓

Report

WHICH FUNCTION DOES EACH JOB?

Read the question.
Tap your answer.

How many supplies are there in all?

We just got 10 more rope.

PUT THE BUILD STEPS IN A SENSIBLE ORDER.

?Run the whole program and check the output
?Write the report that uses the helpers
?Write the helper functions, one at a time
?Write the data: supplies and the crew tree
?Test each helper

WHY THIS EXERCISEBuilding small parts first means each test checks only a little code at a time.

The report calls four helpers: total_items, low_stock, find_item and count_crew. Which helper from the table does it NOT call?

WHY THIS EXERCISErestock changes the data before the report runs, so the report itself does not need it.

Practice lab: decompose the quiz

Part	Job	Function
Questions	Store each question with its answer	make_quiz()
Ask	Show a question and read an answer	ask_one(question)
Check	Compare an answer with the right one	is_right(given, right)
Score	Add up the right answers	score(results)

def is_right(given, right):
    return given == right

def score(results):
    total = 0
    for r in results:
        if r:
            total = total + 1
    return total

print(is_right("8", "8"))
print(is_right("9", "8"))
print(score([True, False, True, True]))

What does the first print line show?

What does the second print line show?

What does the third print line show?

What does score([]) return?

DECOMPOSE CHECK

Read the question.
Tap your answer.

Which function shows a question to the player?

Which part should be built first?

Why give each part its own function?

Statement	True or false?
is_right returns True or False.	?
score counts the False values.	?
The quiz plan has four parts.	?
Decomposing turns one big job into a tree of small jobs.	?

WHY THIS EXERCISEA clear plan makes the build much easier.

What does score([True, True, False]) return?

WHY THIS EXERCISEtotal goes up once for each True.

Decompose your own capstone idea into at least three parts. Give each part a function name.

Super decomposing! A big job is just small jobs in a tree. Tomorrow we choose the right container for each piece of data.