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Workshop 8 — Homework

Welcome to your eighth homework! This week has two big new ideas: modules (borrowing code from Python's standard library, and writing your own files to import) and classes (building your own data type that bundles data together with the functions that work on it). Several tasks build on old homeworks — but now you can reach for ready-made tools and design your own blueprints.

Deadline: before Workshop 9.

How to submit: push everything to the same GitHub repository you used for the previous homeworks, then re-send the repository link to your instructor.

Put this homework in its own folder so it does not mix with the earlier ones:

cd python-homework        # the repo from Homework 1
mkdir workshop_8_homework
cd workshop_8_homework
# ...create your exercise files in here...

When you are done, commit and push from the repository folder:

git add .
git commit -m "Add workshop 8 homework"
git push

If a command fails, read the error message carefully — it usually tells you what is wrong. If you are still stuck, take a screenshot and bring it to the next workshop.

Python exercises

Create the files below and write Python code to solve each task. Use everything we have covered so far: variables, f-strings, input(), int() / float(), if / elif / else, and / or / not, while, for + range(), +=, len(), string methods, lists, dictionaries, tuples, files (open), try / except, comprehensions, def / return — plus this week's new material:

  • Modules — import math, then math.sqrt(x); from random import randint (no dot needed afterwards); import datetime as dt (a shorter nickname). Useful modules: math (sqrt, pi, floor, ceil), random (randint, choice, shuffle), datetime (date.today()), and json (json.dump / json.load to save and load a whole dictionary).
  • Your own module — any .py file is a module. Put functions in one file and import it from another (both in the same folder). The if __name__ == "__main__": guard keeps a file's demo from running when it is imported.
  • Classes — class Dog: is a blueprint; rex = Dog("Rex", 3) builds an object from it. __init__(self, ...) runs when the object is made and stores attributes with self.name = name. A method is a function inside the class whose first parameter is self. Reach attributes and call methods with a dot: rex.name, rex.bark().

Run each file with:

python exercise_1.py

exercise_1.py — Borrow from math

import math and use it to print: the square root of 144, the value of pi, and 7.3 rounded down with math.floor. Label each line.

Example run:

sqrt(144) = 12.0
pi = 3.141592653589793
floor(7.3) = 7

Hint: import math at the top, then math.sqrt(144), math.pi, math.floor(7.3).

exercise_2.py — Roll the dice

from random import randint, choice. Print a random dice roll between 1 and 6, and a random pick from a list of three foods. Run it a few times to see the answers change.

Example run:

You rolled a 4
Tonight: pizza

Hint: randint(1, 6) gives a whole number from 1 to 6 (both ends included); choice(["pizza", "khinkali", "salad"]) picks one item at random.

exercise_3.py — Your own module

Make two files. In shapes.py, write functions square_area(side) and triangle_area(base, height) that return their results. In exercise_3.py, import shapes and print the area of a square and a triangle.

Example run:

Square area: 25
Triangle area: 6.0

Hint: keep both files in the same folder. In exercise_3.py write import shapes, then shapes.square_area(5). Triangle area is base * height / 2.

exercise_4.py — Save a profile with json

Build a dictionary describing yourself (at least name, age, and a list of hobbies). Use json.dump to save it to me.json, then json.load to read it back and print one value from the loaded dictionary.

Example run:

Saved me.json
Loaded back: nino, age 21

Hint: import json. To save: with open("me.json", "w") as f: json.dump(profile, f). To load: with open("me.json") as f: data = json.load(f) — data is a normal dict again, so data["name"] works.

exercise_5.py — Your first class

Define a class Student with an __init__ that stores a name and a grade. Add a method describe(self) that returns a sentence like "nino is in grade 10". Build two students and print each one's description.

Example run:

nino is in grade 10
giorgi is in grade 11

Hint: def __init__(self, name, grade): then self.name = name and self.grade = grade. In describe return an f-string using self.name and self.grade. Build one with s = Student("nino", 10) and call s.describe().

exercise_6.py — A class with behaviour

Define a class Counter that starts at 0. Give it a method increment(self) that adds one, and a method value(self) that returns the current count. Make a counter, increment it three times, and print the value.

Example run:

3

Hint: in __init__ set self.count = 0. increment does self.count += 1. value does return self.count. Call c.increment() three times.

exercise_7.py — A class that protects its data

Define a class Wallet that starts with a balance (default 0). Add add(self, amount) and spend(self, amount). spend must refuse and print a message if the amount is more than the balance, otherwise subtract it. Show both a successful spend and a refused one.

Example run:

Balance: 50
Spent 20. Balance: 30
Cannot spend 100 — only 30 left.

Hint: def __init__(self, balance=0):. In spend, use if amount > self.balance: to refuse, else: to do self.balance -= amount.

exercise_8.py — Notes that remember (bonus)

Combine classes, files, json, and error handling. Write a class NoteBook whose __init__ tries to json.load a list of notes from notes.json (catch FileNotFoundError and start with an empty list if the file is missing). Add a method add(self, note) that appends a note and saves the whole list back with json.dump. Run the program two or three times, adding a note each time, and watch the list grow.

Example first run:

You have 0 note(s).
Add a note: buy milk
Saved!

Example second run:

You have 1 note(s).
1. buy milk
Add a note: call nino
Saved!

Hint: in __init__, wrap the read in try: ... except FileNotFoundError: self.notes = []. In add, do self.notes.append(note) then re-open notes.json in "w" mode and json.dump(self.notes, f).

Checklist before you submit

  • exercise_1.py … exercise_8.py (plus shapes.py) written and run without errors using python exercise_N.py
  • Everything is pushed inside the workshop_8_homework/ folder of your repository
  • You re-sent your repository link to the instructor

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