Graduation challenge · Python from Zero

Why you need it

The intuition

Definition

Decomposition

Decomposition is breaking a program into smaller functions, each solving one part of the problem.

Incremental development

Incremental development means writing a program in small steps and testing after each step.

Examples

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def read_prices():
    n = int(input())
    prices = []
    for i in range(n):
        prices.append(float(input()))
    return prices

def total_with_discount(prices):
    total = sum(prices)
    if total > 15:
        total = total * 0.9
    return round(total, 2)

prices = read_prices()
print(f"Items: {len(prices)}")
print(f"Total: {total_with_discount(prices)}")

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def letter(avg):
    if avg >= 80:
        return "A"
    elif avg >= 65:
        return "B"
    elif avg >= 50:
        return "C"
    return "F"

for test in [95, 70, 50, 10]:
    print(test, letter(test))

Common mistakes

Quick quiz

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def stats(xs):
    return min(xs), max(xs)

low, high = stats([4, 9, 1])
print(high - low)

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print(round(71.666, 1), round(80.0, 1))

Practice

3 exercises in three steps: predict what a program prints, change a program to meet a new requirement, then write one from scratch. Your code runs in the browser and is checked the moment you submit.

1. PredictTrace a whole program

   Type exactly what this program prints.

2. ModifyAdd a discount rule

   Change total_with_discount: over 15 still gets 10% off, but over 50 gets 20% off. Keep round(..., 2).

3. WriteGraduation: grade book

   Read n, then n whole-number scores. Print exactly five lines:

   Count: 3
   Average: 71.7
   Highest: 90
   Lowest: 55
   Grade: B

   • Average is rounded to 1 decimal place with round(avg, 1).
   • Grade is for the average: A for 80+, B for 65+, C for 50+, otherwise F.
   • Write at least one function of your own (for example letter(avg)).

Terms in this lesson