题型分析

Q1: Declare Child Class with Constructor Calling Parent (4–5 marks)

Identify: 题目给出 parent class 代码，要求写 child class 声明和 constructor。

Method:

class Child(Parent):
    def __init__(self, params...):
        super().__init__(parent_params)
        self._new_attr = value

MS Pattern:

• M1 Correct class header: class Child(Parent):
• A1 Constructor method definition with correct parameters def __init__(self, ...):
• A1 Call to super().__init__(...) passing correct parent attributes
• A1 Initialise new child attributes with self._attr = param

Example: w23_qp_42 Q3 — class MagicCharacter(Character):

Traps:

• Forgetting self in super().__init__() — Python does it automatically, DO NOT pass self
• Parameter order must match parent constructor exactly
• Missing colon after class header

Q2: Override Method in Child Class (3–4 marks)

Identify: 要求 override parent 的某个 method，通常需要调用 parent 版本再添加新功能。

Method:

def method_name(self, params...):
    result = super().method_name(params)
    # add child-specific logic
    return result

MS Pattern:

• M1 Method signature matches parent exactly (same name and parameters)
• A1 Call super().method_name(...) to use parent version
• A1 Additional child-specific logic (new attribute / calculation)
• A1 Return value if parent method returned one

Example: s23_qp_41 Q2 — Helicopter.get_info() calls super().get_info() then appends blade info.

Traps:

• Wrong method signature (different number of parameters)
• Not calling super() when required by MS
• Returning wrong type

Q3: Main Program with Both Parent and Child Objects (5 marks)

Identify: 要求写 main program 创建 parent 和 child 对象，调用方法并输出结果。

Method:

def main():
    parent_obj = Parent(params)
    child_obj = Child(params_with_extra)
    print(parent_obj.method())
    print(child_obj.method())  # uses overridden version

MS Pattern:

• A1 Instantiate parent object with correct arguments
• A1 Instantiate child object with correct arguments (including extras)
• M1 Call method on parent object
• A1 Call method on child object (tests overriding)
• A1 Output / print results

Example: s23_qp_42 Q3 — Create Employee and Manager, call calculate_pay() on both.

Traps:

• Mixing up parameter order between parent and child constructors
• Not capturing return value before printing
• Creating child object with wrong number of arguments

Q4: Read File and Create Both Parent / Child Objects Based on Data (7 marks)

Identify: 题目提供数据文件，要求读取、解析、根据标识符创建 parent 或 child 对象。

Method:

def read_data(filename):
    objects = []
    with open(filename, "r") as f:
        for line in f:
            parts = line.strip().split(",")
            if parts[0] == "Parent":
                objects.append(Parent(parts[1], parts[2]))
            elif parts[0] == "Child":
                objects.append(Child(parts[1], parts[2], parts[3]))
    return objects

MS Pattern:

• M1 Open file correctly (with statement or open/close pair)
• A1 Loop to read each line / record
• A1 Split / parse data (e.g. comma-separated)
• A1 Conditional logic to distinguish parent vs child (e.g. if type == "X")
• M1 Create parent object with correct parsed arguments
• A1 Create child object with correct parsed arguments (including extras)
• A1 Store objects in a list and return / process

Example: w23_qp_42 Q3 variant — file contains Character and MagicCharacter records.

Traps:

• Not stripping newline before splitting
• Wrong index access after split
• Forgetting to convert numeric strings to int / float
• File path hardcoded when parameter expected
• Not handling empty lines