private public
預設成員變數、成員方法都是public，除非在成員變數與方法前加上__二個底線，才會變成private。
語法
__二個底線宣告屬性或方法是私有。
私有屬性、私有方法，只供類別內部讀取與寫入，若要提供外部使用，需提供公有public方法供外部呼叫。
class 類別:
__私有屬性 = None
def __私有方法(self):
程式碼
private 屬性
以下宣告__salary私有屬性，並提供get_salary()與set_salary()公有方法供外部使用。
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class Employee:
name = None
__salary = None
def __init__(self, name, salary):
self.name = name
self.__salary = salary
def get_salary(self):
return self.__salary
def set_salary(self, salary):
self.__salary = salary
emp1 = Employee("Mary", 20000)
print(f"name = {emp1.name} salary = {emp1.get_salary()}")
emp1.set_salary(30000)
print(f"name = {emp1.name} salary = {emp1.get_salary()}")
name = Mary salary = 20000
name = Mary salary = 30000
private 方法
私有方法只供內部類別呼叫。
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class Employee:
name = None
level = None
__salary = None
def __init__(self, name, level, salary):
self.name = name
self.level = level
self.__salary = salary
def get_salary(self):
return self.__salary + self.__bonus()
def set_salary(self, salary):
self.__salary = salary
def __bonus(self):
if self.level == 1:
return self.__salary * 0.1
elif self.level == 2:
return self.__salary * 0.2
else:
return self.__salary * 0.3
emp1 = Employee("Mary", 1, 20000)
print(f"emp1 name = {emp1.name} salary = {emp1.get_salary()}")
emp2 = Employee("Bill", 2, 20000)
print(f"emp2 name = {emp2.name} salary = {emp2.get_salary()}")
emp1 name = Mary salary = 22000.0
emp2 name = Bill salary = 24000.0
類別外私有屬性不可指派值
在類別外，私有屬性設值是沒用。
物件.__私有屬性 = 值
以下程式碼，在類別外，設定__salary為50000，但實際輸出仍是20000
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class Employee:
name = None
__salary = None
def __init__(self, name, salary):
self.name = name
self.__salary = salary
def get_salary(self):
return self.__salary
def set_salary(self, salary):
self.__salary = salary
emp1 = Employee("Mary", 20000)
# 以下私有屬性設成50000，無作用
emp1.__salary = "500000"
print(emp1.get_salary())
20000