Converting a list to a dictionary

[Steve Holden]

Drew wrote:
> On Mar 14, 4:52 pm, Bruno Desthuilliers
> <bdesth.quelquech... at free.quelquepart.fr> wrote:
> 
>> res_dict = dict((r.get_id(), r) for r in res_list)
> 
> I'm using Python2.5 and it seems that this only gives me a hash with
> the first id and first record. Am I doing something wrong?
> 
>>>> class Person():
> ...     def __init__(self):
> ...             self.id = 5
> ...
>>>> mylist = []
>>>> for i in range(100):
> ...     mylist.append(Person())
> ...
>>>> mydict = dict((r.id,r) for r in mylist)
>>>> mydict
> {5: <__main__.Person instance at 0x00A99EE0>}
> 
Well, you aren't actually using the object's id() value as the dict key, 
but the value of its id attribute. Since all the instances you create 
have the same value for that attribute each change to the dict (except 
the first) overwrites the immediately preceding change - you can't have 
100 values in a dict all with the same key!

Try:

  >>> mydict = dict((id(r), r) for r in mylist)

and you'll find you then get a dict with 100 elements.

regards
  Steve
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