unpacking vars from list of tuples

Ross rossgk at gmail.com
Wed Sep 16 04:12:05 CEST 2009


Thanks Tim,

That's actually the stuff I was trying to remember.

    my_list = [name for _, name, _ in k]

I recalled using some underscores for nice dense unnamed variable  
unpacking before, but couldn't recall the process.

Thanks for that.

Ross.


On 15-Sep-09, at 6:33 PM, Tim Chase wrote:

>> If I have a list of tuples:
>>    k=[("a", "bob", "c"), ("p", "joe", "d"), ("x", "mary", "z")]
>> and I want to pull the middle element out of each tuple to make a new
>> list:
>> myList = ["bob", "joe", "mary"]
>> is there some compact way to do that?  I can imagine the obvious one
>> of
>> myList = []
>> for a in k:
>>    myList.append(a[1])
>> But I'm guessing Python has something that will do that in one  
>> line...
>
> To add some readability to the other suggested solutions, I'd use
> tuple unpacking
>
>  my_list = [name for status, name, code in k]
>
> Not knowing what [0] and [2] are, I randomly designated them as  
> "status" and "code", but you likely have your own meanings.  If you  
> don't, you can always just use the "_" convention:
>
>   my_list = [name for _, name, _ in k]
>   # or
>   my_list = [name for (_, name, _) in k]
>
> As an aside, "my_list" is preferred over "myList" in common Python  
> practice.  I don't know if there's a preferred convention for "with  
> vs without" the parens in such a tuple-unpacking list comprehension.
>
> -tkc
>
>
>
>
>
>
>




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