透過繼承客製化功能

Python 物件導向程式設計入門

George Boorman

Curriculum Manager, DataCamp

銀行帳戶類別的層級

目前進度

class BankAccount:
    def __init__(self, balance):
       self.balance = balance

    def withdraw(self, amount):
       self.balance -=amount

# Empty class inherited from BankAccount
class SavingsAccount(BankAccount):
    pass

自訂建構式

class SavingsAccount(BankAccount):    
    # Constructor for SavingsAccount with an additional argument
    def __init__(self, balance, interest_rate):  

        # Call the parent constructor using ClassName.__init__()
        # self is a SavingsAccount but also a BankAccount
        BankAccount.__init__(self, balance)

        # Add more functionality
        self.interest_rate = interest_rate

可先用 Parent.__init__(self, args...) 執行父類別建構式
加入更多功能
不一定要呼叫父類別建構式

用自訂建構式建立物件

# Construct the object using the new constructor
acct = SavingsAccount(1000, 0.03)
acct.interest_rate

0.03

加入功能

照常新增方法
可同時使用父類別與子類別的資料

class SavingsAccount(BankAccount):
    def __init__(self, balance, interest_rate):
        BankAccount.__init__(self, balance)
        self.interest_rate = interest_rate

    # New functionality
    def compute_interest(self, n_periods=1):
        return self.balance * ( (1 + self.interest_rate) ** n_periods - 1)

銀行帳戶類別的層級

再加一個子類別

class CheckingAccount(BankAccount):

    def __init__(self, balance, limit):
        BankAccount.__init__(self, balance) # Call the ParentClass constructor
        self.limit = limit

    def deposit(self, amount):
        self.balance += amount

    def withdraw(self, amount, fee=0): # New fee argument

        if amount <= self.limit:
            BankAccount.withdraw(self, amount + fee)  
        else:
            pass # Won't run if the condition isn't met

check_acct = CheckingAccount(1000, 25)

# Will call withdraw from CheckingAccount
check_acct.withdraw(200)


# Will call withdraw from CheckingAccount
check_acct.withdraw(200, fee=15)

bank_acct = BankAccount(1000)

# Will call withdraw from BankAccount
bank_acct.withdraw(200)


# Will produce an error
bank_acct.withdraw(200, fee=15)

TypeError: withdraw() got an unexpected
keyword argument 'fee'

違反多型
- 父／子類別的方法不同

一起來練習吧！

Python 物件導向程式設計入門