python 缓存装饰器

参考https://www.cnblogs.com/faithfu/p/10365868.html

cached_property缓存装饰器

class cached_property(object):
"""
Decorator that converts a method with a single self argument into a
property cached on the instance.
Optional ``name`` argument allows you to make cached properties of other
methods. (e.g.  url = cached_property(get_absolute_url, name='url') )
"""
def __init__(self, func, name=None):
self.func = func
self.__doc__ = getattr(func, '__doc__')
self.name = name or func.__name__

def __get__(self, instance, cls=None):
if instance is None:
return self
res = instance.__dict__[self.name] = self.func(instance)
return res

cached_property主要实现的功能是，user.getWorkYear第一次会进行计算，计算完之后把实例user的__dict__[‘getWorkYear’]设置为计算后的值。下次读值的时候会直接从__dict__[‘getWorkYear’]取结果，避免了多次计算。
使用限制：只能用于只带默认参数的类

不使用的例子

class User(object):
def __init__(self, age=0):
self.age=age

def getWorkYear(self):
return 65-self.age

user=User(20)
print(user.getWorkYear)     #<bound method User.getWorkYear of <__main__.User object at 0x00000000031A3C88>>
print(user.getWorkYear())   #45
print(user.__dict__)  #{'age': 20}
print(user.getWorkYear) #<bound method User.getWorkYear of <__main__.User object at 0x00000000031A3C88>>

使用的例子

from django.utils.functional import cached_property

class User(object):
def __init__(self, age=0):
self.age=age

@cached_property
def getWorkYear(self):
return 65-self.age

user=User(20)
print(user.getWorkYear)    #45
print(user.getWorkYear())  #error
print(user.__dict__)  #{'age': 20, 'getWorkYear': 45}
print(user.getWorkYear) #45
user.getWorkYear -> __get__ -> 从实例字典(user.__dict__`获取 -> 如果没有则保存到字典并调用实际方法返回