[Tutor] Unpacking lists

[Alan Gauld]

On 09/07/14 02:44, Robert Nanney wrote:

> #!/usr/bin/python
> #list_test2.py
>
> list1 = [1, 8, 15]
> list2 = [2, 9, 16]
> list3 = [[3, 4, 5, 6], [10, 11, 12, 13], [17, 18, 19, 20]]
> list4 = [7, 14, 21]
> one_list = zip(list1, list2, list3, list4)
> first_round = [one_list[x][y] for x in range(len(list3)) for y in range(4)]

My first thought is that you are using indexing too much.
The above would be clearer using:

first_round = [tup[x] for tup in one_list for x in range(4)]

> second_round = []
> for i in first_round:
>      if not isinstance(i, list):
>          second_round.append(i)
>      else:
>          for x in range(len(i)):
>              second_round.append(i[x])

and this loop could be
     for item in i:
         second_round.append(item)

But I think list addition would do the job more easily.
Something like (untested)

second_round += i


> While this seems to do the trick, I feel there is probably a
> better/more pythonic way to accomplish the same thing.

I agree but I don;t have time right now to figure it out!
But it seems there should be a more straightforward method.

I'm thinking something like

result = []
for L in (list1,list2,list3):
     if isinstance(L,list)
        result += L
     else: result.append(L)

mebbe...

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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