[Tutor] newB Q: extracting common elements from 2 lists

[Andrei Kulakov]

On Mon, Jun 24, 2002 at 06:51:28AM -0700, Stephen Doughty wrote:
> Hi
> 
> I've just discovered the tutor list, I'm hoping to
> learn a lot more about Python by reading other peoples
> querys/answers.
> 
> My question:
> I'm writing an export script for blender and have
> stuck a hitch. I'm trying to work through the problem
> in IDLE, so the examples are from the command line.
> 
> I have two tuples where the values are lists,
> eg :
> >>> xmap
> {1: [1, 3, 5, 7, 9]}
> >>> ymap
> {1: [1, 2, 3, 4, 5]}
> 
> what I want is to extract the common elements of the
> two tuple values and put them in a new tuple 'list'
> 
> like:
> 
> xymap[1] = xmap[1] *something magic here* ymap[1]
> 
> so xymap[1] contains [1,3,5].
> 
> can it be done?  - as tuples or converted to lists and
> done somehow?
> 
> I found that xymap[1] = xmap[1] and ymap[1] just
> combined the list rather than binary anding them (and
> & caused an error).
> 
> Any advice gratefully received.
> 
> Cheers Stephen
>
One way is to do this:

>>> a = [1, 3, 5, 7, 9]
>>> b = [1, 2, 3, 4, 5]
>>> ab = [x for x in a if x in b]
>>> ab
[1, 3, 5]

Or as a loop:
ab = []
for x in a:
	if x in b:
		ab.append(x)

 - Andrei

> 
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