Python_day9

• 多继承:
  python支持，但不建议使用 

　　　　dir(): 获取类或者对象的方法和属性

　　　　__mro__:获取类的继承顺序

class A(object):
    def run(self):
        print('run A run')

class B(A):
    def run(self):
        super().run()
        print('run B run')

class C(A):
    def run(self):
        super().run()
        print('run C run')

class D(B, C):
    pass


c = C()
c.run()
# 获取类或者对象的方法和属性
print(dir(C))
# 获取类的继承顺序
print(C.__mro__)

d = D()
d.run()
print(D.__mro__)

• python魔法方法

class Student(object):
    def __init__(self, name = 'python'):
        self.__name = name

    def __str__(self):
        '''打印本类对象时，自动调用'''
        return 'hello, %s' % self.__name

    def __repr__(self):
        '''在解释器环境下直接输出本对象，自动调用的方法'''
        return self.__str__()

    def __len__(self):
        '''调用len函数的时候自动调用的方法'''
        return 100

    def __call__(self):
        '''调用本类对象的时候自动调用的方法'''
        print('Student object name:%s' % self.__name)

print(dir(Student))

s = Student()
print(s)

print(len(s))

s()

class Fib(object):
    cnt = 0
    def __init__(self):
        self.a = 0
        self.b = 1

    def __iter__(self):
        '''返回可迭代对象'''
        return self

    def __next__(self):
        '''随着循环自动调用的'''
        self.a, self.b = self.b, self.a+self.b
        
        if self.a >= 100:
            '''循环遍历终止'''        
            raise StopIteration()
        Fib.cnt += 1
        
        return self.a

    def __len__(self):
        return Fib.cnt

    def __getitem__(self, n):
        '''索引时自动调用的方法'''
        if isinstance(n, int):
            a, b = 0, 1
            while n >= 0:
                a, b = b, a+b
                n -= 1
            return a    

        if isinstance(n, slice):
            '''切片类型 start:end'''
            if n.start == None:
                start = 0
            else:
                start = n.start    
            if n.stop == None:
                return 'error'
            stop = n.stop
            l = []
            for i in range(start, stop):
                l.append(self[i])
            return l

f = Fib()

print(dir(f))

for i in f:
    print(i, end=' ')
print()

print(len(f))

for i in range(20):
    print(f[i], end=' ')
print()

print(f[0:3])
print(f[1:10])

• 枚举类

INSERT=1 # 缺点就是本质是变量，可以改变
if choose == INSERT:
    pass

from enum import Enum, unique

@ unique # 防止枚举成员的重复
class Menu(Enum):
    INSERT=1
    DELETE=2
    UPDATE=3
    SHOW=4
    # CHOOSE=4

print(Menu.INSERT.value)
# Menu.INSERT.value = 2
print(Menu['INSERT'])

• 元类(metaclass)

class Test(object):
    def show(self, name='python'):
        print('hello %s', name)

# type()构建一个类

def f(self, name='python'):
    print('hello %s'% name)

Test = type('Test', (object,), dict(show=f))

t = Test()
t.show()

# 另一种构建类的方法，是先构建元类，以元类为模板构建类
class ListMetaclass(type):
    def __new__(cls, name, bases, attrs):
        '''类方法'''
        attrs['add'] = lambda self, value : self.append(value)
        return type.__new__(cls, name, bases, attrs)

class Mylist(list, metaclass=ListMetaclass):
    pass

l = Mylist()
print(type(l))
l.add(1)
l.add('hello')
print(l)