需要下面几行的东西:
class CustomList(List):
def __init__(self):
self.changeID = 0 # This value increases whenever a value is changed in the custom list
我正在寻找一种计算非常便宜的方法来找出列表是否从我上次访问它时更改了它的状态。这样做的方法可能是在每次更新列表的值时更新与列表关联的一些changeID
。
对列表的更改是以下之一:
- 值已追加
- 值已删除
- 值在某个索引处被替换
我所期望的是以下内容:
l1 = CustomList() # changeId = 0 at beginning
l1.append(2) # changeId updates to 1
l1.append(7) # changeId updates to 2
l1.append(30) # changeId updates to 3
l1[1] = 9 # changeId updates to 4 . l1 = [2, 9, 30]
del l1[0] # changeId updates to 5 . l1 = [9,30]
l1.remove(9) # changeId updates to 6 . l1 = [30]
l1.pop() # changeId updates to 7 . l1 = []
print(l1.changeID) # changeID needs to be accessible via the object (of course)
我试图为此编写一些代码,但没有成功。请帮忙。
您将不得不修补个别方法(我可能错过了一些,请做您的研究(:
class CustomList(list):
def __init__(self):
self.change_id = 0
super().__init__()
def append(self, obj):
self.change_id += 1
super().append(obj)
def __setitem__(self, key, value):
self.change_id += 1
super().__setitem__(key, value)
def remove(self, obj):
self.change_id += 1
super().remove(obj)
def pop(self, index):
self.change_id += 1
super().pop(index)
def insert(self, index, obj):
self.chgange_id += 1
super().insert(index, obj)
def __delitem__(self, key):
self.change_id += 1
super().__delitem__(key)
l1 = CustomList()
l1.append(2)
l1.append(7)
l1.append(30)
l1[1] = 9
del l1[0]
l1.remove(9)
l1.pop(0)
print(l1.change_id)
# 7
这段代码有很多重复,我们可以使用一个装饰器:
def increase_change_counter(func):
def inner(self, *args, **kwargs):
self.change_id += 1
return func(self, *args, **kwargs)
return inner
class CustomList(list):
def __init__(self):
self.change_id = 0
super().__init__()
@increase_change_counter
def append(self, obj):
super().append(obj)
@increase_change_counter
def __setitem__(self, key, value):
super().__setitem__(key, value)
@increase_change_counter
def remove(self, obj):
super().remove(obj)
@increase_change_counter
def pop(self, index):
super().pop(index)
@increase_change_counter
def insert(self, index, obj):
super().insert(index, obj)
@increase_change_counter
def __delitem__(self, key):
super().__delitem__(key)
l1 = CustomList()
l1.append(2)
l1.append(7)
l1.append(30)
l1[1] = 9
del l1[0]
l1.remove(9)
l1.pop(0)
print(l1.change_id)
# 7
对于显然是一项简单的任务来说,这仍然太长了。
我们可以试试这个:
class CustomList(list):
def __init__(self):
self.change_id = 0
super().__init__()
def __getattribute__(self, item):
if item in ('append', 'remove', 'pop', 'insert'):
self.change_id += 1
return super().__getattribute__(item)
但是l1[1] = 9
和del l1[0]
不会被__getattribute__
抓住.
所以也许是一个组合:
def increase_change_counter(func):
def inner(self, *args, **kwargs):
self.change_id += 1
return func(self, *args, **kwargs)
return inner
class CustomList(list):
def __init__(self):
self.change_id = 0
super().__init__()
@increase_change_counter
def __setitem__(self, key, value):
super().__setitem__(key, value)
@increase_change_counter
def __delitem__(self, key):
super().__delitem__(key)
def __getattribute__(self, item):
if item in ('append', 'remove', 'pop', 'insert'):
self.change_id += 1
return super().__getattribute__(item)
l1 = CustomList()
l1.append(2)
l1.append(7)
l1.append(30)
l1[1] = 9
del l1[0]
l1.remove(9)
l1.pop(0)
print(l1.change_id)
# 7