insert unique data in a list

[Christian Tismer]

On 12/14/09 2:24 AM, knifenomad wrote:
> On 12월14일, 오전10시19분, knifenomad<knifeno... at gmail.com>  wrote:
>    
>> On 12월14일, 오전2시57분, mattia<ger... at gmail.com>  wrote:
>>
>>
>>
>>
>>
>>      
>>> Il Sun, 13 Dec 2009 16:37:20 +0000, mattia ha scritto:
>>>        
>>      
>>>> How can I insert non-duplicate data in a list? I mean, is there a
>>>> particular option in the creation of a list that permit me not to use
>>>> something like:
>>>> def append_unique(l, val):
>>>>      if val not in l:
>>>>          l.append(val)
>>>>          
>>      
>>>> Thanks,
>>>> Mattia
>>>>          
>>      
>>> Ok, so you all suggest to use a set. Now the second question, more
>>> interesting. Why can't I insert a list into a set? I mean, I have a
>>> function that returns a list. I call this function several times and
>>> maybe the list returned is the same as another one already returned. I
>>> usually put all this lists into another list. How can I assure that my
>>> list contains only unique lists? Using set does'n work (i.e. the python
>>> interpreter tells me: TypeError: unhashable type: 'list')...
>>>        
>> this makes the set type hashable.
>>
>> class Set(set):
>>      __hash__ = lambda self: id(self)
>>
>> s = Set()
>> s.add(1)
>> s.add(2)
>> s.add(1)
>>
>> print s
>> set([1, 2])
>>
>> d = {}
>> d[s] = 'voila'
>>
>> print d
>> {Set([1,2]):'voila'}
>>
>> print d[s]
>> 'voila'- 원본 텍스트 숨기기 -
>>
>> - 원본 텍스트 보기 -
>>      
>
> although it's not what you've asked about. it's intereting to make set
> hashable using __hash__.
Thoughtless messing with __hash__ is seldom useful.

 >>> s1 = Set([1])
 >>> s2 = Set([1])
 >>> s1 == s2
True
 >>> d = {}
 >>> d[s1] = 3
 >>> d[s2] = 5
 >>> d
{Set([1]): 3, Set([1]): 5}
 >>>

Equality is kept for comparison, but what is it worth to hash
them by id?

On the original problem:

You could turn you lists into tuples. This would be clean
and correct.

ciao - chris

-- 
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