Question

在我的程序中，我创建了无休止的类实例。该数量取决于程序运行多长时间。但是，在运行某些代码之后，我根本不需要这些实例。我如何才能将它们从内存中完全删除？

简单的示例代码：

class Player:
    def __init__(self, color):
        self.color = color

for n in range(1000):
    p = Player('black')

在这种情况下，del p是否会完全删除该实例？

Answer 1

在这种情况下，del p仅会删除对Player对象的 reference ，以便以后可以由垃圾收集器将其拾取。

但是，当超出范围时也会发生这种情况。

在大多数日常Python中，无需使用显式的del语句。

Answer 2

Python中无法删除实例。取而代之的是，您可以删除对实例的引用，一旦引用全部消失，则将回收该对象。

Answer 3

当不再引用它们时，Python会将它们从内存中删除。如果您有Player个实例引用了其他Player个实例（例如：p.teammates = [list of Players]），则可能会以循环引用结尾，这可能会阻止它们被垃圾回收。在这种情况下，您应该考虑使用weakref模块。

例如：

>>>sam = Player('blue')
>>>rob = Player('green')
>>>sam.team = [sam, rob]
>>>rob.team = [sam, rob]
>>> #sam and rob may not be deleted because they contain 
>>> #references to eachother so the reference count cannot reach 0
>>>del sam #del is a way to manually dereference an object in an interactive prompt. Otherwise the interpreter cannot know you won't use it again unlike when the entire code is known at the beginning.
>>>print(rob.team[0].color) #this prints 'blue' proving that sam hasn't been deleted yet
blue

那我们该如何解决呢？

>>>sam = Player('blue')
>>>rob = Player('green')
>>>sam.team = [weakref.ref(sam), weakref.ref(rob)]
>>>rob.team = [weakref.ref(sam), weakref.ref(rob)]
>>> #now sam and rob can be deleted, but we've changed the contents of `p.team` a bit:
>>> #if they both still exist:
>>>rob.team[0]() is sam #calling a `ref` object returns the object it refers to if it still exists
True
>>>del sam
>>>rob.team[0]() #calling a `ref` object that has been deleted returns `None`
None
>>>rob.team[0]().color #sam no longer exists so we can't get his color
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'color'

从内存中删除类实例

3 个答案: