参考：
https://segmentfault.com/a/1190000007256392
本文地址:https://htmonster.xyz/blog/post/python_magicmethod/
简介
- 被 __ 包围的方法 称为魔术方法
构造与初始化
-
__init__对象初始化时候调用 将传入的参数初始化实例 返回None -
__new__对象初始化时候调用 创建类并返回类的实例 返回实例
属性访问与控制
__getattr__(self,name)定义访问一个不存在的属性时的行为__setattr__(self,name,value)定义对属性进行复制和修改操作时的行为__delattr__(self,name)定义删除属性的行为__getattribute__(self,name)定义自己的属性被访问时候的行为
class Access(object):
def __getattr__(self, name):
print '__getattr__'
return super(Access, self).__getattr__(name)
def __setattr__(self, name, value):
print '__setattr__'
return super(Access, self).__setattr__(name, value)
def __delattr__(self, name):
print '__delattr__'
return super(Access, self).__delattr__(name)
def __getattribute__(self, name):
print '__getattribute__'
return super(Access, self).__getattribute__(name)
access = Access()
access.attr1 = True # __setattr__调用
access.attr1 # 属性存在,只有__getattribute__调用
try:
access.attr2 # 属性不存在, 先调用__getattribute__, 后调用__getattr__
except AttributeError:
描述器对象
描述器对象不能独立存在，需要被另一个所有者持有。
描述器要实现以下的三种方法
-
__get__(self,instance,owner)对其读值时候调用 -
__set__(self,instance,value)对其修改值时候调用 -
__delete__(self,instance)对其删除时候调用
class Meter(object):
'''Descriptor for a meter.'''
def __init__(self, value=0.0):
self.value = float(value)
def __get__(self, instance, owner):
return self.value
def __set__(self, instance, value):
self.value = float(value)
class Foot(object):
'''Descriptor for a foot.'''
def __get__(self, instance, owner):
return instance.meter * 3.2808
def __set__(self, instance, value):
instance.meter = float(value) / 3.2808
class Distance(object):
meter = Meter()
foot = Foot()
d = Distance()
print d.meter, d.foot # 0.0, 0.0
d.meter = 1
print d.meter, d.foot # 1.0 3.2808
d.meter = 2
print d.meter, d.foot # 2.0 6.5616
