[Tutor] Looking for duplicates within a list [SOLVED]

[Ken G.]

Hugo Arts wrote:
> On 11 jun 2010, at 17:49, Steven D'Aprano <steve at pearwood.info> wrote:
>
>   
>> On Sat, 12 Jun 2010 12:58:19 am Alan Gauld wrote:
>>
>>     
>>> Have you looked at the count method of lists?
>>>
>>> Something like:
>>>
>>> counts = set(( item, mylist.count(item)) for item in mylist if
>>> mylist.count(item) > 1)
>>>       
>> That's a Shlemiel the Painter algorithm.
>>
>> http://www.joelonsoftware.com/articles/fog0000000319.html
>>
>>     
>
> It is, but it's also very elegant and simple to understand. And it
> works fine on small inputs. Everything is fast for small n.
>
>   
>>> Seems to work...
>>>       
>> You say that now, but one day you will use it on a list of 100,000
>> items, and you'll wonder why it takes 45 minutes to finish, and curse
>> Python for being slow.
>>
>>     
>
> Actually, now that you know it is a shlemiel the painter's algorithm,
> you won't have to wonder anymore. And you'll just say: "well, this
> piece of code might need to handle huge lists someday, I'll use a
> dictionary."
>
> I guess what I'm trying to say is: using code that performs bad in
> situations that won't be encountered anyway is not inherently bad.
> Otherwise, we'd all still be writing everything in C.
>
> The corrolary, of course, is that you should always know what the
> performance characteristics of your code are, and what kind of data it
> will handle.
>
> Hugo
>
>   
I appreciate your input.  Thanks!

Ken
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