面向对象练习题

面向对象练习题

1、实现单例模式

姿势1,利用classmethod实现

class Mysql:
	__instance = None
	def __init__(self, host="127.0.0.1", post=9999):
		self.host = host
		self.post = post
		

	@classmethod
	def single(cls,):
		if not cls.__instance:
			cls.__instance = cls()
		return cls.__instance



sql1 = Mysql()
sql2 = Mysql()
print(sql1 is sql2)
sql3 = Mysql.single()
sql4 = Mysql.single()
print(sql3 is sql4)

姿势2，自定义元类

class Mymeta(type):
	__instance = None
	# def __init__(self, *args, **kwargs):
	# 	super().__init__(*args, **kwargs)
	def __call__(self, *args, **kwargs):
		if not self.__instance:
			super().__call__(*args, **kwargs)
		# print('__instance',self.__instance)
		return self.__instance



class Mysql(metaclass=Mymeta):
	def __init__(self, host='127.0.0.1', post=9999):
		self.host = host
		self.post = post


a = Mysql()
b = Mysql()
print(a is b )

姿势3

class Singleton:
	__instance = None
	def __new__(self, *args, **kwargs):
		if not self.__instance:
			super().__new__(self, *args, **kwargs) 


p1 = Singleton()
p2 = Singleton()
print(p1 is p2)

2、编写程序, 在元类中控制把自定义类的数据属性都变成大写

class Mymeta(type):
	def __new__(cls,name, bases, dics):
		update_dic = {}
		for k,v in dics.items():
			if not callable(v) and not k.startswith("__"):
				update_dic[k.upper()] = v
			else:
				update_dic[k] = v
		return type.__new__(cls,name, bases, update_dic)


class Chinese(metaclass=Mymeta):
	country = "china"
	sex = 'male'

print(Chinese.__dict__)

3、编写程序, 在元类中控制自定义的类无需init方法.

class MyMeta(type):
	def __call__(self, *args, **kwargs):
		if args:
			raise typeError("must be keyword argument")

		obj = object.__new__(self)
		for k, v in kwargs.items():
			obj.__dict__[k]=v
		return obj

class Chinese(metaclass=MyMeta):
	country = 'china'


p1 = Chinese(name='alex', age=18)
print(p1, p1.country)
print(p1.__dict__)

4、编写程序, 编写一个学生类, 要求有一个计数器的属性, 统计总共实例化了多少个学生.

class Student:
	i = 0
	def __init__(self, name):
		self.name = name
		Student.i += 1
		
	
	@classmethod
	def count(cls):
		
		return cls.i
		

		

a = Student("a")
b = Student("b") 
print(Student.count())

5、编写程序, A 继承了 B, 俩个类都实现了 handle 方法, 在 A 中的 handle 方法中调用 B 的 handle 方法

class B:
	def handle(self):
		print("B handle")


class A(B):
	def handle(self):
		super(A, self).handle()
		print("a handle")



a = A()
a.handle()