【Python】面向对象 - 封装 ② ( 访问私有成员 | 对象无法访问私有变量 / 方法 | 类内部访问私有成员 )

韩曙亮

发布于 2023-10-11 11:45:18

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代码可运行

文章被收录于专栏：韩曙亮的移动开发专栏韩曙亮的移动开发专栏

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代码可运行

一、访问私有成员

1、对象无法访问私有变量

在下面的 Python 类 Student 中 , 定义了私有的成员变量 ,

    # 定义私有成员
    __address = None

该私有成员变量 , 只能在类内部进行访问 , 类的外部无法进行访问 ;

在类外部创建的 Student 实例对象 , 是无法访问 __address 私有成员的 ;

使用实例对象访问类的私有成员 , 编译时不会报错 , 但是运行时会报错

AttributeError: 'Student' object has no attribute '__address'. Did you mean: 'address'?

最后一行代码

print(s1.__address)

访问 s1 实例对象的 __address 成员 , 会报如下错误 ;

代码示例 :

"""
面向对象 - 封装
"""


# 定义 Python 类
class Student:
    name = None
    age = None

    def say(self):
        print(f"{self.name} is {self.age} years old")

    # 定义私有成员
    __address = None

    # 定义私有成员方法
    def __say(self):
        print(f"地址是 {self.__address}")

    def __init__(self, name, age, address):
        self.name = name
        self.age = age
        self.address = address


# 创建对象
s1 = Student("Tom", 18, "学院路6号")
print(s1.name)
print(s1.age)
print(s1.__address)

执行结果 :

Y:\002_WorkSpace\PycharmProjects\pythonProject\venv\Scripts\python.exe Y:/002_WorkSpace/PycharmProjects/HelloPython/hello.py
Traceback (most recent call last):
  File "Y:\002_WorkSpace\PycharmProjects\HelloPython\hello.py", line 31, in <module>
    print(s1.__address)
AttributeError: 'Student' object has no attribute '__address'. Did you mean: 'address'?
Tom
18

Process finished with exit code 1

2、对象无法访问私有方法

在类中定义私有成员方法

    # 定义私有成员方法
    def __say(self):
        print(f"地址是 {self.__address}")

创建对象 , 调用该私有成员方法 ,

# 创建对象
s1 = Student("Tom", 18, "学院路6号")
s1.__say()

报如下错误 :

AttributeError: 'Student' object has no attribute '__say'

代码示例 :

"""
面向对象 - 封装
"""


# 定义 Python 类
class Student:
    name = None
    age = None

    def say(self):
        print(f"{self.name} is {self.age} years old")

    # 定义私有成员
    __address = None

    # 定义私有成员方法
    def __say(self):
        print(f"地址是 {self.__address}")

    def __init__(self, name, age, address):
        self.name = name
        self.age = age
        self.address = address


# 创建对象
s1 = Student("Tom", 18, "学院路6号")
print(s1.name)
print(s1.age)
s1.__say()

执行结果 :

Y:\002_WorkSpace\PycharmProjects\pythonProject\venv\Scripts\python.exe Y:/002_WorkSpace/PycharmProjects/HelloPython/hello.py
Tom
18
Traceback (most recent call last):
  File "Y:\002_WorkSpace\PycharmProjects\HelloPython\hello.py", line 31, in <module>
    s1.__say()
AttributeError: 'Student' object has no attribute '__say'

Process finished with exit code 1

3、类内部访问私有成员

在 Student 类中 , 定义了私有成员变量和私有成员方法 :

    # 定义私有成员
    __address = None

    # 定义私有成员方法
    def __say(self):
        print(f"address is {self.__address}")

并且在 say 成员方法中 , 调用了上述私有的成员变量和成员方法 :

    def say(self):
        print(f"{self.name} is {self.age} years old , address is {self.__address}")
        self.__say()

最终的执行结果为 :

Tom is 18 years old , address is 学院路6号
address is 学院路6号

完整代码示例 :

"""
面向对象 - 封装
"""


# 定义 Python 类
class Student:
    name = None
    age = None

    def say(self):
        print(f"{self.name} is {self.age} years old , address is {self.__address}")
        self.__say()

    # 定义私有成员
    __address = None

    # 定义私有成员方法
    def __say(self):
        print(f"address is {self.__address}")

    def __init__(self, name, age, address):
        self.name = name
        self.age = age
        self.__address = address


# 创建对象
s1 = Student("Tom", 18, "学院路6号")
print(s1.name)
print(s1.age)
s1.say()

执行结果 :

Y:\002_WorkSpace\PycharmProjects\pythonProject\venv\Scripts\python.exe Y:/002_WorkSpace/PycharmProjects/HelloPython/hello.py
Tom
18
Tom is 18 years old , address is 学院路6号
address is 学院路6号

Process finished with exit code 0