Python Programming Unit 4

Object-Oriented Python

Model programs with classes, objects, methods, and collections of objects.

This unit introduces object-oriented programming in Python. Students work with classes, objects, instance variables, methods, constructors, string representations, encapsulation, composition, object relationships, collections of objects, and small system design. The unit also connects Python vocabulary to Java and AP Computer Science A ideas so students can transfer concepts across languages without confusion.

Who This Unit Is For

Best for Python students preparing for larger projects, Java/AP CSA readiness, game simulations, inventory systems, gradebooks, or app-style data models.

Learning Goals

Define classes with constructors, instance variables, and methods.
Explain how an object stores its own state.
Use string representations to make objects easier to inspect while debugging.
Model relationships between objects with composition and collections.
Connect Python OOP vocabulary to Java/AP CSA class and object vocabulary.

Key Concepts

What students practice in this unit

Objects help students manage programs that have many related values. A gradebook, library tracker, game, or simulation becomes easier to reason about when each concept has a clear class and set of responsibilities.

Classes and objects

Students learn that a class is a blueprint and each object has its own data.

Methods and state

Students write methods that read or update instance variables in controlled ways.

Composition

Students build systems where one object can contain or coordinate other objects.

Collections of objects

Students practice lists of Student, Course, Book, or GameCharacter objects and process them with loops.

Practice

Exercises and mini-project ideas

These are public practice prompts students can use to strengthen the unit without exposing the full internal lesson sequence.

Practice Exercises

Create a Student class with name, grade level, scores, and an average method.
Create a Course class that stores students and reports class-level summaries.
Build a Gradebook that can add scores and find students who need review.
Model inventory items with price, quantity, and restock checks.
Create a GameCharacter with health, points, and action methods.
Build a LibraryBook tracker with checkout and return methods.

Mini-Project Ideas

Mini gradebook with Student and Course classes.
Inventory tracker that flags low-stock items.
Simple simulation using objects for players, tasks, or events.

Short Example

class Student:
    def __init__(self, name, scores):
        self.name = name
        self.scores = scores

    def average(self):
        return sum(self.scores) / len(self.scores)

    def __str__(self):
        return f"{self.name}: {self.average():.1f}"

student = Student("Ari", [92, 88, 95])
print(student)

Common Student Mistakes

Forgetting to use self when reading or changing instance variables.
Confusing a class variable with an instance variable.
Making every variable public without thinking about valid updates.
Writing one large class that handles every part of the program.
Creating objects but then storing the same information again in separate lists.

Challenge Extension

Students draw a small class diagram before coding and explain which object owns which piece of data.

How This Prepares the Next Step

Students are ready to store object data in files, load records from CSV or JSON, and automate workflows around structured information.

Related Code Scholars Paths

AP Computer Science A

Ready to practice?

Build Python skills with a guided plan.

Students can use this page for review, then work with Code Scholars on targeted exercises, debugging support, projects, and next-step planning.

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