Object-Oriented Programming
Home Lesson 3 — Using Objects

Q3 is the prerequisite check. Every loop in this lesson walks through an array by index. An off-by-one range either misses the last object or crashes past the end — examiners report it in seven of the last ten series.

Emma
Emma 474
<__main__.Book object at 0x…>

• Shelf[1].GetTitle() reads left to right: take the array, pick element 1, call its method. Element 1 is the second book, because indexes start at 0.
• Longest is a whole Book object, not a number and not a title. It starts as the first book and is replaced whenever a longer one turns up. Because it is an object, you can call its methods — Longest.GetTitle() — after the loop. The loop starts at 1 because element 0 is already in Longest; there is no point comparing it with itself.
• The last line prints the object itself, and Python has no idea how you want a book shown, so you get its type and memory address. An object is not its data. To output what is inside it, call a method: a get method, or a Display… method. Printing a whole object or list instead of the values inside it is a recurring output error in the examiner reports.

def TotalPages():
    Total = 0
    for Index in range(0, 3):
        Total = Total + Shelf[Index].GetPages()
    return Total

def FindBook(SearchTitle):
    for Index in range(0, 3):
        if Shelf[Index].GetTitle() == SearchTitle:
            return Index
    return -1

print("Total pages: " + str(TotalPages()))

Position = FindBook("Holes")
if Position == -1:
    print("Holes is not on the shelf")
else:
    print("Holes is at index " + str(Position))

Position = FindBook("Beloved")
if Position == -1:
    print("Beloved is not on the shelf")
else:
    print("Beloved is at index " + str(Position))

• The functions go outside the class — they work with books, they are not part of one. They can read Shelf because it is declared in the main program.
• In FindBook, return -1 is lined up with the for, not the if. It runs only once the loop has checked every book.
• Position = FindBook(...) calls the search once and keeps the answer. Writing if FindBook("Holes") != -1: and then calling FindBook again inside the if does all the work twice — and when a call changes something, calling it twice is a real bug that examiners report in five series.

• ✗ range(0, 2) misses the last book. It visits indexes 0 and 1 only. Three books need range(0, 3).
• ✗ Total = 0 is inside the loop. It is reset on every pass, so it can never hold more than one book's pages. Initialise once, before the loop.
• ✗ return is inside the loop. The function hands back its answer after the first book and stops — the loop never gets a second pass. That is why the answer is 412 ÷ 3.
• ✓ Shelf[Index].GetPages() — array, element, method, and the returned value is used. That line is credited.

def AveragePages():
    Total = 0
    for Index in range(0, 3):
        Total = Total + Shelf[Index].GetPages()
    return Total / 3

The habit to build: for every line in a loop question, ask "once, or every time?" Setting up a total happens once — before. Adding to it happens every time — inside. Returning the answer happens once — after. The indentation of that line is your answer to the question.

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 self.__Name

    def GetCredits(self):
        return self.__Credits

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

    def AddCredits(self, Amount):
        NewTotal = self.__Credits + Amount
        if NewTotal > 50:
            NewTotal = 50
        self.__Credits = NewTotal

Accepted alternatives

• MP1–MP2: building the array with ClubMembers = [] and append, as long as the type is evidenced and the order matches the indexes.
• MP3: five separate AddCredits calls, or a loop over a second array of credit values.
• MP4: for Index in range(0, 5) or range(5). Looping with for M in ClubMembers: is accepted for (b), but (c) must return an index, so it needs one.

Not credited, however good the code looks

• A loop of range(0, 4) — MP4 lost; Mia is never counted.
• Total = 0 or return inside the loop — MP4 or MP6 lost.
• if ClubMembers[Index] == SearchName — MP8 lost, and nothing is ever found.
• return -1 in an else inside the loop — MP10 lost; only the first member can be found.
• print(ClubMembers[2]) instead of calling DisplayDetails() — MP13 lost.
• Code pasted as an image — no code marks at all.

Extension — not counted in the 15

• E1 "Best so far" starts as the first element (ClubMembers[0]), not as 0 or an empty value.
• E2 …compares GetCredits() of each remaining element with the best so far, and replaces it when greater.
• E3 Returns the object, after the loop.
• E4 Called once; the returned object is stored and its get methods produce Most credits: Lina Haddad (50).