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题型分析

Q1: Declare class with private attributes + constructor (4-5 marks)​

Identify: 题目要求 "declare a class"、"constructor"、"private attributes"

Standard method:

  1. class ClassName:
  2. def __init__(self, ...):
  3. self.__attr = param（每个 private attribute 一行）
  4. 有时需要初始化默认值 self.__count = 0
MS Pattern
  • M1: Correct class declaration with class keyword and colon
  • A1: Correct __init__ method signature with self as first parameter
  • A1: Each private attribute correctly assigned with self.__attr = param
  • B1: Any additional default attribute correctly initialised
Example: 9618/s24/qp/41 Q2
class Employee:
    def __init__(self, empID, empName):
        self.__empID = empID
        self.__empName = empName
        self.__salary = 0.0
Example: 9618/w22/qp/41 Q2
class Character:
    def __init__(self, name, health):
        self.__name = name
        self.__health = health
        self.__maxHealth = health

Traps:

  • 忘记 self 参数 → 0 marks for constructor line
  • Private attribute 必须用 __（双下划线）而不是单下划线
  • 拼写错误：attribute 名称必须和题目完全一致

Q2: Implement getter methods (3 marks)​

Identify: "getter"、"accessor"、"return the value of"

Standard method:

  1. def GetAttrName(self):
  2. return self.__attr
MS Pattern
  • M1: Correct method signature with self parameter
  • A1: Use of return keyword
  • A1: Correctly references self.__attr
Example: 9618/s24/qp/41 Q2
def GetEmpID(self):
    return self.__empID
Example: 9618/w23/qp/42 Q2
def GetTitle(self):
    return self.__title

Traps:

  • 用了 print 而不是 return → 扣 1 mark
  • 遗漏 self. → 写成 return __attr

Q3: Implement setter methods (3 marks)​

Identify: "setter"、"mutator"、"update/change the value of"

Standard method:

  1. def SetAttrName(self, value):
  2. self.__attr = value
  3. 有时需要 validation（如 if value >= 0）
MS Pattern
  • M1: Correct method signature with self and parameter
  • A1: Correct assignment self.__attr = value
  • B1: Validation / range check where required
Example: 9618/s24/qp/41 Q2
def SetSalary(self, salary):
    if salary >= 0.0:
        self.__salary = salary
Example: 9618/w22/qp/41 Q2
def SetHealth(self, health):
    if 0 <= health <= self.__maxHealth:
        self.__health = health

Traps:

  • 题目要求 validation 但没写 → 扣 B1 mark
  • setter parameter name 和 attribute name 混淆

Q4: Create objects and call methods (2-4 marks)​

Identify: "instantiate"、"create an object"、"call the method"

Standard method:

  1. obj = ClassName(args)
  2. obj.MethodName()
MS Pattern
  • M1: Correct object instantiation with class name and arguments
  • A1: Correct method call on object using dot notation
Example: 9618/s24/qp/41 Q2
emp1 = Employee("E001", "Alice")
emp1.SetSalary(3500.0)
print(emp1.GetEmpName())
Example: 9618/s23/qp/41 Q2
player1 = Character("Hero", 100)
player1.TakeDamage(20)

Traps:

  • 对象名必须和题目要求一致（如 myObject 而不是随便起名）
  • constructor 参数顺序错误

Q5: Array of objects with file reading (7 marks)​

Identify: "read from file"、"array/list of objects"、"store in array"

Standard method:

  1. Open file: file = open("data.txt", "r")
  2. Loop through lines: for line in file.readlines():
  3. Split line: data = line.strip().split(",")
  4. Create object: obj = ClassName(data[0], data[1])
  5. Append to list: arr.append(obj)
  6. Close file: file.close()
MS Pattern
  • M1: Correct file opening with mode "r"
  • M1: Write a loop to read all lines from file
  • A1: Correct use of strip() and split() to parse data
  • A1: Create new object and add to list
  • B1: File is closed after reading
Example: 9618/s24/qp/42 Q2
def ReadEmployees():
    empList = []
    file = open("employees.txt", "r")
    for line in file.readlines():
        data = line.strip().split(",")
        emp = Employee(data[0], data[1], data[2])
        empList.append(emp)
    file.close()
    return empList
Example: 9618/w22/qp/42 Q2
def LoadStudents():
    students = []
    file = open("students.txt", "r")
    for line in file.readlines():
        parts = line.strip().split(",")
        s = Student(parts[0], parts[1], int(parts[2]))
        students.append(s)
    file.close()
    return students

Traps:

  • 忘记 strip() — 换行符 \n 会残留 → 数据错误
  • 忘记类型转换 — 文件读取的都是 string，数字需要 int() 或 float()
  • 忘记 file.close() — 可能只扣 1 mark 但必须写

Q6: Business logic using object methods (6 marks)​

Identify: "calculate"、"display all"、"find the highest"、"process"

Standard method:

  1. Loop through array of objects
  2. Call getter methods to access data
  3. Implement logic (sum, max, count, display)
  4. Return or print result
MS Pattern
  • M1: Loop through all objects in array
  • A1: Correct use of method calls to access data
  • A1: Correct logic (accumulation / comparison / condition)
  • A1: Return or output the result
Example: 9618/s24/qp/41 Q2
def CalculateTotalSalary(empList):
    total = 0.0
    for emp in empList:
        total += emp.GetSalary()
    return total
Example: 9618/w23/qp/41 Q2
def DisplayHighScorers(playerList):
    for player in playerList:
        if player.GetScore() >= 80:
            print(player.GetName(), player.GetScore())

Traps:

  • 直接用 emp.__salary 而不是通过 getter → 正确但违反 encapsulation 原则，考试允许但推荐用 getter
  • 循环外要初始化累加器 total = 0
  • 比较最大值时用 > 时注意初始值设为 None 或第一个元素