继承比较与字符串表示
Python 面向对象编程入门
George Boorman
Curriculum Manager, DataCamp
比较不同类的对象
class Customer:
def __init__(self, acc_id, name):
self.acc_id, self.name = acc_id, name
def __eq__(self, other):
# 当对象属性相同且类型相同返回 True
return (self.acc_id == other.acc_id) and (self.name == other.name)\
and (type(self) == type(other))
带继承的对象比较
如果一个对象从另一个对象的类中继承，会怎样？
银行账户与储蓄账户
父类/子类中的 __eq__
class BankAccount:
def __init__(self, number, balance=0):
self.balance = balance
self.number = number
def withdraw(self, amount):
self.balance -= amount
# 定义 __eq__：当号码相等时返回 True
def __eq__(self, other):
print("BankAccount __eq__() called")
return self.number == other.number
class SavingsAccount(BankAccount):
def __init__(self, number, balance, interest_rate):
BankAccount.__init__(self, number,
balance)
self.interest_rate = interest_rate
# 定义 __eq__：当号码相等时返回 True
def __eq__(self, other):
print("SavingsAccount __eq__() called")
return self.number == other.number
比较父类与子类对象
ba = BankAccount(123, 10000)
sa = SavingsAccount(456, 2000, 0.05)
# 比较两个对象
ba == sa
SavingsAccount __eq__() called
False
sa == ba
SavingsAccount __eq__() called
False
打印对象
class Customer:
def __init__(self, name, balance):
self.name, self.balance = name, balance
cust = Customer("Maryam Azar", 3000)
print(cust)
<__main__.Customer at 0x1f8598e2240>
a_list = [1,2,3]
print(a_list)
[1, 2, 3]
__str__()
print(obj),str(obj)
print(np.array([1,2,3]))
[1 2 3]
str(np.array([1,2,3]))
'[1 2 3]'
- 非正式，面向最终用户
- 字符串表示
__repr__()
repr(obj)，控制台打印
repr(np.array([1,2,3]))
'array([1,2,3])'
np.array([1,2,3])
array([1, 2, 3])
- 正式，面向开发者
- 可复现的表示
print()的后备
实现：repr
class Customer: def __init__(self, name, balance): self.name = name self.balance = balance def __repr__(self):# 注意 name 周围的引号 return f"Customer('{self.name}', {self.balance})"cust = Customer("Maryam Azar", 3000) # 会隐式调用 __repr__() cust
Customer('Maryam Azar', 3000)
实现：str
class Customer:
def __init__(self, name, balance):
self.name = name
self.balance = balance
def __str__(self):
cust_str = f"""
Customer:
name: {self.name}
balance: {self.balance}
"""
return cust_str
cust = Customer("Maryam Azar", 3000)
# 会隐式调用 __str__()
print(cust)
Customer:
name: Maryam Azar
balance: 3000
开始练习吧！
Python 面向对象编程入门
