[Tutor] selecting elements from dictionary

[Evert Rol]

> using:
> 
> for key, value in xdic.items():
>     if 1 in value and 2 in value or 3 in value:
>         print key
> 
> 
> also print keys that have values such as [1,2,3]. 
> 
> In cases where there is [1,2,3] and [1,2] also reported. 
> 
> How can I extract those keys that have values only [1,2] and [1,3] exclusively.  

If you know that elements in a list are unique (so only appear once), you may want to look at using sets.

  Evert


> >>> xdic = {75796988: [1, 2, 3], 75797478: [1, 2, 3], 75797887:[1,2], 75797987:[3,1]}
> >>> for key, value in xdic.items():
> ...     if 1 in value and 2 in value or 3 in value:
> ...             print key
> ...
> 75797987
> 75796988
> 75797478
> 75797887
> 
> 
> Here all 4 keys appear. Instead I want to get only 75797887:[1,2] and 75797987:[3,1]
> how can I force this. 
> 
> thanks again. 
> 
> 
> 
> 
> 
> From: Steven D'Aprano <steve at pearwood.info>
> To: tutor at python.org
> Sent: Wed, September 15, 2010 7:27:05 AM
> Subject: Re: [Tutor] selecting elements from dictionary
> 
> On Wed, 15 Sep 2010 12:10:59 pm Hs Hs wrote:
> 
> > I want to print only those items that have [1,2] and [1,3]  in any
> > order, such as [1,2] or [2,1], [3,1] or [1,3]
> >
> > >>> for item in xdic.keys():
> >
> > ...    if [1,2] in xdic[item]:
> > ...            print item
> >
> > I get a wrong answer, 
> 
> That's because you ask the wrong question.
> 
> [1,2] in xdic[item] doesn't check to see if 1 is in the list, then if 2 
> is in the list. It looks to see if one of the items is *exactly* [1,2].
> 
> >>> [1,2] in [1,2,3,4]
> False
> >>> [1,2] in [1,2,3,4, [1,2]]
> True
> 
> 
> > I know the values are there. How can I print 
> > only those item that have [1,2] and [1,3]
> 
> for key, value in xdic.items():
>     if 1 in value and 2 in value or 3 in value:
>         print key
> 
> 
> 
> 
> -- 
> Steven D'Aprano
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