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

[lina]

<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?

> ...       weight[elem.__repr__()] += 1
> ...   else:
> ...       weight[elem.__repr__()] = 1
> ...
>>>> weight
> {"['34', '58', '34', '58']": 1, "['61', '70', '61', '34']": 1, "['61', '34',
> '61
> ', '34']": 1, "['61', '35', '61', '70', '61']": 1}
>
> or
>
>>>> from collections import defaultdict
>>>> list1 = [['61', '34', '61', '34'], ['61', '35', '61', '70', '61'],
>>>> ['61', '7
> 0', '61', '34'], ['34', '58', '34', '58']]
>>>> weight = defaultdict(int)
>>>> for elem in list1:
> ...     weight[elem.__repr__()] += 1
> ...
>>>> weight
> defaultdict(<type 'int'>, {"['34', '58', '34', '58']": 1, "['61', '70',
> '61', '34']": 1, "['61', '34', '61', '34']": 1, "['61', '35', '61', '70',
> '61']": 1})
>
> Hope that helps.
>
> --
>
> Christian Witts
> Python Developer
>