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