我有以下Python程序:
import weakref
class NumberWord:
def __init__(self,word):
self.word = word
def __repr__(self):
return self.word
dict = weakref.WeakValueDictionary()
print(f"[A] {len(dict)}")
print(f"dict.get(0) = {dict.get(0)}")
print(f"dict.get(1) = {dict.get(1)}")
list = []
list.append(NumberWord("zero"))
dict[0] = list[0]
print(f"[B] {len(dict)}")
print(f"dict.get(0) = {dict.get(0)}")
print(f"dict.get(1) = {dict.get(1)}")
list.append(NumberWord("one"))
dict[1] = list[1]
print(list)
print(f"[C] {len(dict)}")
print(f"dict.get(0) = {dict.get(0)}")
print(f"dict.get(1) = {dict.get(1)}")
list.pop()
print(list)
print(f"[D] {len(dict)}")
print(f"dict.get(0) = {dict.get(0)}")
print(f"dict.get(1) = {dict.get(1)}")
list.pop()
print(list)
print(f"[E] {len(dict)}")
print(f"dict.get(0) = {dict.get(0)}")
print(f"dict.get(1) = {dict.get(1)}")
我期望以下行为:
-
在步骤[A]中,字典为空
-
在步骤[B]中,字典包含
dict[0] = NumberWord("zero")
-
在步骤[C]中,字典包含
dict[0] = NumberWord("zero")
和dict[1] = NumberWord("one")
-
在步骤[D]中,字典包含
dict[1] = NumberWord("one")
(由于列表中唯一的强引用已消失,因此删除了“零”) -
在步骤[E]中,字典再次为空(由于列表中唯一的强引用消失了,因此删除了“一个”)
一切正常, 步骤[E]:“一个”不会不会消失。为什么不呢?
这是实际输出:
>>> import weakref
>>>
>>> class NumberWord:
... def __init__(self,word):
... self.word = word
... def __repr__(self):
... return self.word
...
>>> dict = weakref.WeakValueDictionary()
>>>
>>> print(f"[A] {len(dict)}")
[A] 0
>>> print(f"dict.get(0) = {dict.get(0)}")
dict.get(0) = None
>>> print(f"dict.get(1) = {dict.get(1)}")
dict.get(1) = None
>>>
>>> list = []
>>> list.append(NumberWord("zero"))
>>> dict[0] = list[0]
>>>
>>> print(f"[B] {len(dict)}")
[B] 1
>>> print(f"dict.get(0) = {dict.get(0)}")
dict.get(0) = zero
>>> print(f"dict.get(1) = {dict.get(1)}")
dict.get(1) = None
>>>
>>> list.append(NumberWord("one"))
>>> dict[1] = list[1]
>>> print(list)
[zero,one]
>>>
>>> print(f"[C] {len(dict)}")
[C] 2
>>> print(f"dict.get(0) = {dict.get(0)}")
dict.get(0) = zero
>>> print(f"dict.get(1) = {dict.get(1)}")
dict.get(1) = one
>>>
>>> list.pop()
one
>>> print(list)
[zero]
>>>
>>> print(f"[D] {len(dict)}")
[D] 2
>>> print(f"dict.get(0) = {dict.get(0)}")
dict.get(0) = zero
>>> print(f"dict.get(1) = {dict.get(1)}")
dict.get(1) = one
>>>
>>> list.pop()
zero
>>> print(list)
[]
>>>
>>> print(f"[E] {len(dict)}")
[E] 1
>>> print(f"dict.get(0) = {dict.get(0)}")
dict.get(0) = zero
>>> print(f"dict.get(1) = {dict.get(1)}")
dict.get(1) = None
>>>
>>>