繼承下的比較與字串表示
Python 物件導向程式設計入門
George Boorman
Curriculum Manager, DataCamp
比較不同類別的物件
class Customer:
def __init__(self, acc_id, name):
self.acc_id, self.name = acc_id, name
def __eq__(self, other):
# Returns True if the objects have the same attributes
# and are of the same type
return (self.acc_id == other.acc_id) and (self.name == other.name)\
and (type(self) == type(other))
在繼承下比較物件
若其中一個物件從另一個物件的類別「繼承」，該怎麼辦？
往來與儲蓄帳戶
__eq__ 在父類別與子類別中
class BankAccount:
def __init__(self, number, balance=0):
self.balance = balance
self.number = number
def withdraw(self, amount):
self.balance -= amount
# Define __eq__ that returns True
# if the number attributes are equal
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
# Define __eq__ that returns True
# if the number attributes are equal
def __eq__(self, other):
print("SavingsAccount __eq__() called")
return self.number == other.number
比較父類別與子類別物件
ba = BankAccount(123, 10000)
sa = SavingsAccount(456, 2000, 0.05)
# Compare the two objects
ba == sa
SavingsAccount __eq__() called
False
sa == ba
SavingsAccount __eq__() called
False
列印物件
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]'
- 較非正式，給終端使用者
- 字串（str）表示
__repr__()
repr(obj)、在主控台列印
repr(np.array([1,2,3]))
'array([1,2,3])'
np.array([1,2,3])
array([1, 2, 3])
- 較正式，給開發者
- 可再現（reproducible）的表示（representation）
print()的後備選項
實作：repr
class Customer: def __init__(self, name, balance): self.name = name self.balance = balance def __repr__(self):# Notice the '...' around name return f"Customer('{self.name}', {self.balance})"cust = Customer("Maryam Azar", 3000) # Will implicitly call __repr__() cust
Customer('Maryam Azar', 3000)
實作：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)
# Will implicitly call __str__()
print(cust)
Customer:
name: Maryam Azar
balance: 3000
一起來練習吧！
Python 物件導向程式設計入門
