python 面向对象的一些魔法方法和反射

1.with和__enter__,__exit__,__init__配合使用
class A:
def __init__(self):
print('init')

def __enter__(self):
print('before')

def __exit__(self, exc_type, exc_val, exc_tb):
print('after')

def __new__(cls, *args, **kwargs):
print('in new function')
return object.__new__(A)

with A() as a:
print('123')

结果：in new function,init,before,123,after

2.__del__ 析构方法，当对象在内存中被释放时，自动触发执行

3.__str__和__repr__ 改变对象的字符串显示__str__,__repr__
class B:

def __str__(self):
return 'str : class B'

def __repr__(self):
return 'repr : class B'

b = B()
print('%s' % b)
print('%r' % b)

4.对象的四个可以实现自省的函数hasattr，getattr，setattr，delattr
class Foo:
f = '类的静态变量'
def __init__(self,name,age):
self.name=name
self.age=age

def say_hi(self):
print('hi,%s'%self.name)

obj=Foo('egon',73)

#检测是否含有某属性
print(hasattr(obj,'name'))
print(hasattr(obj,'say_hi'))

#获取属性
n=getattr(obj,'name')
print(n)
func=getattr(obj,'say_hi')
func()

print(getattr(obj,'aaaaaaaa','不存在啊')) #报错

#设置属性
setattr(obj,'sb',True)
setattr(obj,'show_name',lambda self:self.name+'sb')
print(obj.__dict__)
print(obj.show_name(obj))

#删除属性
delattr(obj,'age')
delattr(obj,'show_name')
delattr(obj,'show_name111')#不存在,则报错