Object-Oriented Programming
Home Lesson 2 — Get and Set Methods

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How this lesson works

Same routine as last week. This page teaches, then makes you type — and this week you build on the Member class you wrote in Lesson 1.

1. Learn on this page. Predict what code will do, run it here in the browser, then pick it apart. Nothing to install.
2. Open your Lesson 1 code. Your assessed task adds new methods to your own Member class. If you did not finish Lesson 1, there is a starting version in the task section — use it rather than stopping.
3. Evidence it. Paste your code as text and your screenshot into this week's Evidence Document, and submit it on Teams.

Retrieval

Do Now — three minutes, no notes

Answer these before you read anything else. Write them in your book, then reveal the answers and mark them.

Where this is going

Learning objectives

Vocabulary

Key terms — learn these wordings

Written the way a mark scheme writes them. Learn the wording, not the gist.

PRIMM · Step 1

Predict

Read this program carefully. Do not run it yet. Two methods that look almost identical. Write down exactly what you think the program will output, line by line.

class Book:
    def __init__(self, Title, Year):
        self.__Title = Title        # STRING
        self.__Year = Year          # INTEGER

    def GetTitle(self):
        return self.__Title

    def ShowTitle(self):
        print(self.__Title)

MyBook = Book("Dune", 1965)
A = MyBook.GetTitle()
B = MyBook.ShowTitle()
print("A is", A)
print("B is", B)

PRIMM · Step 2

Run

Now run it. Press Run and compare the real output with your prediction. Python runs inside this page — nothing is sent anywhere.

Press Run to execute.

Your code and your prediction are saved in this browser, so closing the tab does not lose them. If a program never finishes, press Stop.

Dune
A is Dune
B is None

MyBook.GetTitle()

PRIMM · Step 3

Investigate — return, output, get, set

1. The question tells you which one it wants

Before you write a method, find the verb in the question or the class design. It is an instruction, not a figure of speech.

2. A get method — three rules

def GetYear(self):
    return self.__Year

• No parameter other than self. The object already holds the value; there is nothing to pass in. A get method with a parameter is the most repeated OOP error on Paper 4.
• One return, of the attribute.
• Unchanged. No input, no assignment, no print. A get method that also changes the attribute is not a get method.

3. A set method — two rules

def SetYear(self, NewYear):
    self.__Year = NewYear

• Exactly one parameter after self — the new value. Not input() inside the method: the value arrives through the parameter.
• Attribute on the left, parameter on the right. NewYear = self.__Year runs without an error and changes nothing. Read every assignment right-to-left: "take NewYear, put it into Year".

4. The two set methods that separate the grades

Paper 4 does not stop at "replace the value". Two variants come up, and they are where the marks spread out.

Add to — the parameter is an amount to add, not the new value:

def AddPoints(self, Amount):
    self.__Points = self.__Points + Amount

Writing self.__Points = Amount here throws away everything the object already had. Read the design: "adds Amount to Points" is not "sets Points to Amount".

Clamp — add, but never go past a limit. The order is everything: add first, then limit, then store.

def AddPoints(self, Amount):
    NewTotal = self.__Points + Amount     # 1. add
    if NewTotal > 100:                    # 2. limit
        NewTotal = 100
    self.__Points = NewTotal              # 3. store

Trace it with Points at 90 and a call of AddPoints(30):

Adding straight into the attribute and then correcting it (self.__Points = self.__Points + Amount, then if self.__Points > 100: self.__Points = 100) is also fine — the value left stored is still limited. What matters is that the limit is applied to the new total, after the addition.

PRIMM · Step 4

Modify

Go back to the runner and change the program to do the following.

class Book:
    def __init__(self, Title, Year):
        self.__Title = Title        # STRING
        self.__Year = Year          # INTEGER

    def GetTitle(self):
        return self.__Title

    def GetYear(self):
        return self.__Year

    def SetYear(self, NewYear):
        self.__Year = NewYear

MyBook = Book("Dune", 1956)
MyBook.SetYear(1965)
Published = MyBook.GetYear()
BookAge = 2026 - Published
print(MyBook.GetTitle() + " is " + str(BookAge) + " years old")

The marks

Exam technique — the verb is the instruction

A game stores each player as an object. The design says:

Predict, then reveal. A candidate writes this. Decide what an examiner would credit before you open the answer.

    def GetHealth(self, Health):
        print(self.__Health)

    def Heal(self, Amount):
        if self.__Health > 100:
            self.__Health = 100
        self.__Health = self.__Health + Amount

    def GetHealth(self):
        return self.__Health

    def Heal(self, Amount):
        NewHealth = self.__Health + Amount
        if NewHealth > 100:
            NewHealth = 100
        self.__Health = NewHealth

Assessed work

Over to you — extend your Member class

Everyone starts at Independent. Drop to Scaffolded if you stall. Go to Exam Conditions when you have finished.

class Member:
    def __init__(self, MemberID, Name, Age):
        self.__MemberID = MemberID   # STRING
        self.__Name = Name           # STRING
        self.__Age = Age             # INTEGER
        self.__Credits = 0           # INTEGER
        self.__Active = True         # BOOLEAN

    def DisplayDetails(self):
        print("Member ID : " + self.__MemberID)
        print("Name      : " + self.__Name)
        print("Age       : " + str(self.__Age))
        print("Credits   : " + str(self.__Credits))
        print("Active    : " + str(self.__Active))

    def GetName(self):
        return ______

    def GetCredits(______):
        # ... one line

    def SetAge(self, ______):
        self.__Age = ______

    def AddCredits(self, Amount):
        NewTotal = ______ + ______        # 1. add
        # ... 2. limit: if the new total is over 50, make it 50
        # ... 3. store the new total in the attribute

# ---- main program ----
# ... create the object with the test data, in a variable called TheMember
# ... call SetAge on it with 17
# ... call AddCredits twice: 30, then 35
print(TheMember.GetName() + " has " + str(______) + " credits")
# ... call DisplayDetails on it

Self-marking

Mark scheme — open it only after you have attempted the task

Mark your own work honestly against this, then record your total in the Evidence Document.

Hand-in

What to submit on Teams

One file: the Evidence Document for this lesson, saved as .docx and named Surname Initial — OOP Home Lesson 2.docx.

Your next taught lesson opens by checking these submissions. If you got stuck, submit what you have with a note saying where — that is far more useful to me than nothing.

Coming next

Home Lesson 3 — Using objects. Not one member but a whole club: an array of objects, a loop over it, and doing something with every value your get methods hand back. This is the skill examiners currently name as the national weakness on Paper 4, and today's lesson is the foundation for it.