8. 类和对象

基于网络课程《Python全栈开发专题》 记录笔记，请支持正版课程。

创建一个类

self， 即this。带self的是实例方法，否则是静态方法

class Person:
    
    def setName(self, name):
        self.name = name

    def getName(self):
        return self.name

    def greet(self):
        print("Hello, I'm {name}".format(name = self.name))

person = Person()
person.setName('二狗')
person.greet()

方法的私有化

方法名前加"__"双下划线
“伪私有化”：其实质是吧方法名改成了_Class__methodName的形式

class Person:
    def method1(self):
        print('method1')

    # _Class__methodName
    def __method2(self):
        print('method2')

person = Person()
person.method1()
# 报错
# person.__method2()

# 正确的调用姿势
person._Person__method2()

import inspect

methods = inspect.getmembers(person, predicate = inspect.ismethod)
for method in methods:
    print(method)

'''
输出：
('_Person__method2', >)
('method1', >)
'''

类代码块

class MyClass:
    print('MyClass')
    count = 0
    def counter(self):
        self.count += 1

my = MyClass()
my.counter()
print(my.count)
'''
输出：
MyClass
1
'''

类的继承 + 检测类的继承关系

class ParentClass:
    def method1(self):
        print('method 1')

class ChildClass(ParentClass):
    def method2(self):
        print('method 2')

class SubClass(ChildClass):
    pass

parent = ParentClass()
child = ChildClass()
child.method1()
child.method2()

print(issubclass(ChildClass, ParentClass))  # True
print(issubclass(ParentClass, ChildClass))  # False

# Java: instanceof
print(isinstance(child, ParentClass))  # True
print(isinstance(child, ChildClass))   # True

print(ChildClass.__base__)
print(SubClass.__bases__)

Python类的多继承

如果有同名的方法，以继承时定义的顺序为准

class Calculator:
    def calculate(self, expression):
        self.value = eval(expression)
    def printResult(self):
        print('result: {}'.format(self.value))

class MyPrint:
    def printResult(self):
        print('计算结果: {}'.format(self.value))

class NewCalculator(Calculator, MyPrint):
    pass

class NewCalculator2(MyPrint, Calculator):
    pass

c1 = NewCalculator()
c1.calculate('1 + 1')
c1.printResult()

c2 = NewCalculator2()
c2.calculate('1 + 2')
c2.printResult()

print(NewCalculator.__bases__)
print(NewCalculator2.__bases__)

接口

# hasattr  getattr  setattr

class MyClass:
    def method1(self):
        print('method1')
    def method2(self):
        print('method2')
    def default(self):
        print('default')

myClass = MyClass()

if hasattr(myClass, 'method1'):
    myClass.method1()
else:
    print('method1方法不存在！')

getattr(myClass, 'method2')()
# 不存在的方法，返回default
getattr(myClass, 'method21', myClass.default)()

def fun():
    print('fun')

# 默认值可以指定成一个别的函数
getattr(myClass, 'asdf', fun)()

def process():
    print('动态添加的process方法')

setattr(myClass, 'abc', process)
myClass.abc()

myClass1 = MyClass()
# setattr 是添加到实例里，另外一个实例就不能用的
# myClass1.abc()