有没有一种简单的方法可以在对象级别上记住(和刷新)Python上的属性? [英] Is there an easy way to memoize (and flush) properties on Python at object level?

问题描述

我正在寻找一种缓存对象属性的方法.就我而言，我假设对象可以随时间变化，因此该属性的备注值应可刷新.在纯python中，我希望具有以下行为:

I'm looking for a way to cache properties of an object. In my case, I suppose the object can change over the time, so the memoized value for the property should be flushable. In pure python, I want to have a behaviour like:

class Foo:
  def __init__(self, text: str):
    self._text  = text
    self._bar = None

  def flush(self):
     self._bar = None

  def update_text(self, text: str):
     self._text = text 
     self.flush()

  @property
  def bar(self):
    if self._bar is None:
      print('Computing bar...')
      self._bar = f'Computation with "{self._text}".'
    return self._bar

foo1 = Foo('Dog')
foo2 = Foo('Fish')

print(foo1.bar)
# Computing bar...
# Computation with "Dog".

print(foo1.bar)
# Computation with "Dog".

print(foo2.bar)
# Computing bar...
# Computation with "Fish".

print(foo2.bar)
# Computation with "Fish".

foo1.update_text('Cat')

print(foo1.bar)
# Computing bar...
# Computation with "Cat".

print(foo1.bar)
# Computation with "Cat".

print(foo2.bar)
# Computation with "Fish".

然后，如您所见，我想缓存 Foo.bar 属性.我的方法是定义一个私有属性，将其初始化为 None ，然后进行分配和刷新以获取记录的行为.

Then, as you can see, I want to cache the Foo.bar property. My approach was to define a private property initialised as None and then assigned and flushed to obtain a memoized behaviour.

现在，我的问题是，是否有某种方法，库，方法或技术可以在无需拥有私有属性的情况下获得此行为(假设您在类中倾向于记忆的属性).

我正在从标准库(@lru_cache()装饰器(以及最新的 @cached_property )的信息.python.org/3/library/functools.html"rel =" nofollow noreferrer> https://docs.python.org/3/library/functools.html )，但我意识到cache_clear()方法删除该类的所有实例的备注值.

I was reading about the @lru_cache() decorator (and the newest @cached_property) from the Standard Library (https://docs.python.org/3/library/functools.html), but I realised that the cache_clear() method removes the memoized values for all the instances of the class.

我本以为一种可能的解决方案可能是使用不可变对象，但这种解决方案并非我所希望的，因为在某些情况下，我只想刷新属性备注之一.

I was thinking that one possible solution could be to use immutable objects, but that solution is not as I want, because probably there will be situations in which I only want to flush one of the properties memoization.

推荐答案

感谢@sanyash对问题评论的讨论.

有一个 cached_property 包( https://pypi.org/project/cached-property/)来提供请求的行为.使用 cached_property 的示例如下:

There is a cached_property package (https://pypi.org/project/cached-property/) that provides the requested behaviour. The example using cached_property is as follows:

from cached_property import cached_property


class Foo:

    def __init__(self, text: str):
        self._text = text

    def flush(self):
        del self.__dict__['bar']

    def update_text(self, text: str):
        self._text = text
        self.flush()

    @cached_property
    def bar(self):
        print('Computing bar...')
        return f'Computation with "{self._text}".'


foo1 = Foo('Dog')
foo2 = Foo('Fish')

print(foo1.bar)
# Computing bar...
# Computation with "Dog".

print(foo1.bar)
# Computation with "Dog".

print(foo2.bar)
# Computing bar...
# Computation with "Fish".

print(foo2.bar)
# Computation with "Fish".

foo1.update_text('Cat')

print(foo1.bar)
# Computing bar...
# Computation with "Cat".

print(foo1.bar)
# Computation with "Cat".

print(foo2.bar)
# Computation with "Fish".

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