7.13. 方法的动态特性

7.13.1. 可以将外部函数 动态的添加到类中

代码示例

#!/usr/bin/env python
#-*- coding:utf8 -*-
class Fruit(object):
    pass

def add(self):          #定义在类外的函数
    print("grow...")

if __name__ == '__main__':
    Fruit.grow = add            #将函数加到方法中
    fuit = Fruit()              #实例化类
    fuit.grow()                 #调用类中的方法

#!/usr/bin/env python
#-*- coding:utf8 -*-
class Fruit():
    def grow(self):
        print("grow....")

def update():
    print("grow..........")

if __name__ == '__main__':
    fruit = Fruit()
    fruit.grow()
    fruit.grow = update     #使用update函数来更新方法
    fruit.grow()

#!/usr/bin/env python
#-*- coding:utf8 -*-

def square(arg):
    return arg ** 2

class Sum:
    def __init__(self,val):
        self.val = val

    def __call__(self, arg):
        return self.val + arg


class Product:
    def __init__(self, val):
        self.val = val

    def method(self, arg):
        return self.val * arg


if __name__ == '__main__':
    sobject = Sum(2)
    poject = Product(3)

actions = [square, sobject, poject.method]

for act in actions:
    print(act(5))

print(actions[-1](5))
print([act(5) for act in actions])
print(list(map(lambda act:act(5),actions)))

table = {act(5): act for act in actions}
print(table.keys())
print(table.values())
print(table.items())

7.13.2. 使用type函数动态创建类

#!/usr/bin/env python
# -*- coding:utf8 -*-
# auther; 18793
# Date：2019/6/14 13:09
# filename: 使用type函数动态创建类.py
def fn(self):
    print("fn函数")


# 使用type()定义Dog类
Dog = type("Dog", (object,), dict(walk=fn, age=6))

"""
参数1：创建的类名
参数2：继承的父类集合，必须要有一个逗号
参数3：字典对象，key为变量名或者方法名，value如果是函数代表方法，如果是普通值，代表类变量
"""

#創建Dog对象
d = Dog()

#分别查看d、Dog的类型
print(type(d))
print(type(Dog))
d.walk()
print(Dog.age)

7.13.3. 使用metaclass 定义统一特性方法

#!/usr/bin/env python
# -*- coding:utf8 -*-
# auther; 18793
# Date：2019/6/14 13:59
# filename: 使用metaclass.py

# metaclass类的__new__方法的作用就是：当丞相使用class定义新类时，如果指定了metaclass，那么metaclass的__new__方法就会被自动执行

class ItemMetaClass(type):
    def __new__(cls, name, bases, attrs):
        # 为该类动态添加一个cal_price方法
        attrs['cal_price'] = lambda self: self.price * self.discount
        return type.__new__(cls, name, bases, attrs)


# 定义Book类
class Book(metaclass=ItemMetaClass):
    __slots__ = ["name", "price", "_discount"]

    def __init__(self, name, price):
        self.name = name
        self.price = price

    @property
    def discount(self):
        return self._discount

    @discount.setter
    def discount(self, discount):
        self._discount = discount


# 定义CellPhone
class CellPhone(metaclass=ItemMetaClass):
    __slots__ = ["price", "_discount"]

    def __init__(self, price):
        self.price = price

    @property
    def discount(self):
        return self._discount

    @discount.setter
    def discount(self, discount):
        self._discount = discount


if __name__ == '__main__':
    b = Book("python入门到精通", 99)
    b.discount = 0.95
    # 创建Book对象的cal_price()方法
    print(b.cal_price())

    hu = CellPhone(2000)
    hu.discount = 0.85
    # 创建CellPhone对象的cal_price()方法
    print(hu.cal_price())

输出信息

94.05
1700.0