defaultdict相当于列表 [英] defaultdict equivalent for lists
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问题描述
有没有_如何建立等效的python非常有用的 集合.defaultdict
?
想象这种容器的使用:
>>> a = collections.defaultlist(0)
>>>> a [2] = 7
>>>> a [4] ='x'
>>>> a
[0,07,0,'x']
UPDATE:我添加了一个后续问题以添加更多这个结构的功能
解决方案
我认为这会有点混乱的使用;然而,这里是我对如何做的第一个想法:
class defaultlist(list):
def __init __ ,fx):
self._fx = fx
def __setitem __(self,index,value):
while len(self)< = index:
self .append(self._fx())
list .__ setitem __(self,index,value)
当我运行时:
a = defaultlist(int)
print a
a [2] = 7
a [4] ='x'
我回来了:
[]
[0,0,7,0,'x']
Is there\How would you build an equivalent of python's very useful collections.defaultdict
?
Imagined usage of such a container:
>>> a = collections.defaultlist(0)
>>> a[2]=7
>>> a[4]='x'
>>> a
[0,0,7,0,'x']
UPDATE: I've added a follow up question to add even more functionality to this construct
解决方案
I think this would be a bit confusing to use; however, here's my first thought on how to do it:
class defaultlist(list):
def __init__(self, fx):
self._fx = fx
def __setitem__(self, index, value):
while len(self) <= index:
self.append(self._fx())
list.__setitem__(self, index, value)
This takes a callable (I think that's how defaultdict works) for the default value.
When I run:
a = defaultlist(int)
print a
a[2] = 7
a[4] = 'x'
print a
I get back:
[]
[0, 0, 7, 0, 'x']
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