[Tutor] how to understand unhashable type: 'list'

[Christian Witts]

On 2011/11/17 03:56 PM, lina wrote:
> <snip>
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>>
>> sum(1 if type(elem) == list else 0 for elem in list1) not work for you if
>> all you want to do is count how many lists you have in your main list ?
>>
>> not count how many sublists in the main list.
>>
>> wanna count the occurence of the sublists,
>>
>> I mean, something like
>>
>> dictionary[list1[1]]=occurence
>>
>> Traceback (most recent call last):
>>    File "<pyshell#298>", line 1, in<module>
>>      dictionary[list1[1]]=1
>> TypeError: unhashable type: 'list'
>>
>> dictionary[list1[1]]=1
>>
>> Traceback (most recent call last):
>>    File "<pyshell#298>", line 1, in<module>
>>      dictionary[list1[1]]=1
>> TypeError: unhashable type: 'list'
>>
>>
>> For that you'll need to convert your list to a hash-able type if you want to
>> use dictionaries for your store, easiest would probably to use the string
>> representation for it so you could do
>>
>>>>> list1 = [['61', '34', '61', '34'], ['61', '35', '61', '70', '61'],
>>>>> ['61', '70', '61', '34'], ['34', '58', '34', '58']]
>>>>> weight = {}
>>>>> for elem in list1:
>> ...   if elem.__repr__() in weight:
> This is cool.
>
> May I ask which role the __repr__ plays here?
>
>
__repr__ is the string representation of a Python object [1] so I'm 
using it to create something that is hash-able to be used as the 
dictionary key value.

[1] http://docs.python.org/library/functions.html#repr

-- 

Christian Witts
Python Developer
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