解题方法

1. Class Structure 通用模板

class ClassName:
    def __init__(self, param1, param2, ...):
        # private attributes
        self.__attr1 = param1
        self.__attr2 = param2
        # public / protected attributes
        self._counter = 0

    # --- Getter Methods ---
    def GetAttr1(self):
        return self.__attr1

    # --- Setter Methods ---
    def SetAttr1(self, value):
        # validation (if required)
        if condition:
            self.__attr1 = value

    # --- Other Methods ---
    def MethodName(self, args):
        # business logic
        return result

2. Constructor __init__

• 必须有 self 作为第一个参数
• 每个 attribute 都用 self.__name = ... 初始化
• 题目要求 "initialise to 0" → self.__count = 0
• 题目要求 "initialise to empty string" → self.__name = ""

备注

考试中 所有 attribute 都是 private，除非题目明确要求 public（极少）。

变量命名对照表

题目用语	Python 写法
private attribute name	self.__name
public attribute count	self.count
protected attribute id	self._id
constructor with 2 params	def __init__(self, a, b)
default value	self.__x = 0

3. Getter / Accessor Method

def GetAttributeName(self):
    return self.__attributeName

• Method name 通常 Python 风格：Get...（PascalCase）
• 如果返回的是 boolean，有时用 Is...（如 IsAvailable()）
• 必须用 return，不能只用 print

4. Setter / Mutator Method

def SetAttributeName(self, value):
    if condition:  # optional validation
        self.__attributeName = value

• Setter 参数名可以和 attribute 不同以区分
• 常见 validation：>= 0、0 <= x <= 100、.isnumeric()
• 有时没有 validation，直接赋值即可

5. Object 创建与方法调用

# Create object
obj = ClassName(arg1, arg2)

# Call getter
result = obj.GetAttr()

# Call setter
obj.SetAttr(newValue)

# Call other methods
obj.DoSomething()

6. Array / List of Objects

# Empty list
arr = []

# Add objects
arr.append(obj1)
arr.append(obj2)

# Access via index
first = arr[0]
print(first.GetName())

# Loop through all
for item in arr:
    print(item.GetName())

7. Composition (一个 class 包含另一个 class)

class Engine:
    def __init__(self, power):
        self.__power = power

class Car:
    def __init__(self, model, enginePower):
        self.__model = model
        self.__engine = Engine(enginePower)  # composition

    def GetModel(self):
        return self.__model

• 在 constructor 中创建 "has-a" 对象
• 外部通过 getter 访问内部对象

8. File I/O with Objects

# --- Read from file to array of objects ---
def LoadData(filename):
    arr = []
    file = open(filename, "r")
    for line in file.readlines():
        parts = line.strip().split(",")
        # 类型转换：string → int/float
        obj = ClassName(parts[0], int(parts[1]))
        arr.append(obj)
    file.close()
    return arr

# --- Write array of objects to file ---
def SaveData(filename, arr):
    file = open(filename, "w")
    for obj in arr:
        file.write(obj.GetName() + "," + str(obj.GetValue()) + "\n")
    file.close()

数据解析要点

• CSV 格式：line.strip().split(",")
• 空格分隔：line.strip().split()
• 固定宽度：string slicing line[0:5]